Integrated active-matrix light emitting pixel arrays based devices

ABSTRACT

Integrated active-matrix light emitting pixel arrays based displays and methods of fabricating the integrated displays are provided. One of the methods includes: forming a plurality of light emitting elements on a substrate, each of the light emitting elements including multiple semiconductor layers epitaxially grown on the substrate and being configured to emit light with a single color, integrating the light emitting elements formed on the substrate with a backplane device, such that each of the light emitting elements is bonded and conductively coupled to a respective pixel circuit in the backplane device, and then removing the substrate from the light emitting elements that remain integrated with the backplane device. Active-matrix multi-color pixel arrays can be formed by sequentially integrating different color light emitting element arrays on the backplane device or depositing different color phosphor or quantum dot materials on single color light emitting element arrays integrated on the backplane device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims priority toU.S. patent application Ser. No. 16/601,542, filed on Oct. 14, 2019. Theentirety of the disclosure of the prior application is hereinincorporated by reference.

TECHNICAL FIELD

This disclosure relates generally to display devices or systems,particularly to integrated active-matrix light emitting pixel arraysbased display devices or systems.

BACKGROUND

Displays utilizing arrays of light emitting pixels are popular in theelectronic field and especially in portable electronic and communicationdevices, because large amounts of data and pictures can be transmittedrapidly and virtually to any location. Light emitting diode (LED) arraysare becoming more popular than liquid crystal displays (LCD) as an imagesource in both direct view and virtual image displays. One reason forthis is that LEDs are capable of generating relatively high luminance,thus displays incorporating LED arrays can be used in a greater varietyof ambient conditions.

Although LED arrays offer certain advantages, a major disadvantage isthe complexity of their manufacturing process. In some cases, the arraysare manufactured by depositing materials on a supporting substrate andaddressing/driver connections to row and column buses are made aroundthe edges. Thus, the supporting substrate size is larger than the arraysize because of the necessary I/O pads or terminals. Providing verysmall contact pads in an effort to increase the array size greatlyreduces the assembly yield. Another problem is that the driver circuitryfor the LED arrays has a relatively high power consumption and adds afurther manufacturing complexity.

SUMMARY

Described herein are integrated active-matrix light emitting pixel arraybased devices or systems and methods of making them, for example, byintegrating arrays of light emitting elements formed on substrates withbackplane devices followed by removal of the substrates of the lightemitting elements, which can greatly simplify the manufacturingcomplexity and improve manufacturing efficiency and quality.

Described herein are integrated active-matrix light emitting pixel arraybased devices or systems and methods of making them, for example, byintegrating arrays of light emitting elements formed on substrates withbackplane devices followed by removal of the substrates of the lightemitting elements, which can greatly simplify the manufacturingcomplexity and improve manufacturing efficiency and quality.

One aspect of the present disclosure features a method of fabricating anintegrated device, including: forming a plurality of first lightemitting elements on a first substrate, each of the first light emittingelements including first semiconductor layers epitaxially grown on thefirst substrate and being configured to emit light with a first color,the first semiconductor layers including a first conductive outer layeron a side of the first semiconductor layers further from the firstsubstrate; integrating the first light emitting elements formed on thefirst substrate with a backplane device having a plurality of pixelcircuits by bonding the first conductive outer layers of the first lightemitting elements with conductive outer layers of first pixel circuitsin the plurality of pixel circuits such that each of the first lightemitting elements is bonded and conductively coupled to a first pixelcircuit in the backplane device, where the plurality of pixel circuitsare conductively isolated from each other; and then after integratingthe first light emitting elements, removing the first substrate from thefirst light emitting elements that remain integrated with the backplanedevice.

In some implementations, integrating the first light emitting elementson the first substrate with the backplane device includes: before thebonding, pretreating with plasma activation at least one of surfaces ofthe first conductive outer layers of the first light emitting elementsor a surface of the backplane device including surfaces of theconductive outer layers of the first pixel circuits.

In some implementations, forming a plurality of first light emittingelements on a first substrate includes: patterning a first lightemitting structure formed on the first substrate to form the pluralityof first light emitting elements, where the first light emittingstructure includes the first semiconductor layers epitaxially grown onthe first substrate. In some examples, patterning a first light emittingstructure formed on the first substrate to form the plurality of firstlight emitting elements includes: patterning the first light emittingstructure formed on the first substrate according to a pattern of thefirst pixel circuits in the backplane device, such that each of thefirst light emitting elements is aligned and bonded on top of the firstpixel circuit in the backplane device.

In some implementations, integrating the first light emitting elementson the first substrate with the backplane device includes directlybonding surfaces of the first conductive outer layers of the first lightemitting elements with surfaces of conductive outer layers of the firstpixel circuits.

The method can further include: before the integrating, aligning thefirst light emitting elements with the first pixel circuits. Aligningthe first light emitting elements with the first pixel circuits caninclude: aligning the first light emitting elements on the firstsubstrate with the first pixel circuits in a first region of thebackplane device. Integrating the first light emitting elements on thefirst substrate with the backplane device can include: bonding the firstlight emitting elements on the first substrate with the first pixelcircuits in the first region of the backplane device. The method canfurther include: bonding another plurality of first light emittingelements on another first substrate with respective another first pixelcircuits in a second region of the backplane device, the second regionbeing adjacent to the first region; and removing the another firstsubstrate from the another plurality of first light emitting elementsthat remain bonded on the backplane device.

In some implementations, removing the first substrate from the firstlight emitting elements includes: scanning, by using a laser, an area onthe first substrate such that the first light emitting elements in thearea are separated from the first substrate and bonded on the backplanedevice; and lifting off the first substrate from the first lightemitting elements that remain bonded on the backplane device.

A size of the first light emitting element can be no smaller than a sizeof the first pixel circuit. Each of the pixel circuits can include anon-volatile memory including at least one transistor conductivelycoupled to a corresponding drive electrode that is a conductive outerlayer of the pixel circuit, the corresponding drive electrodes inadjacent pixel circuits being separated by dielectric spacers, and eachof the first light emitting elements can include a corresponding contactelectrode as the first conductive outer layer, and each of the firstlight emitting elements can be conductively coupled to a non-volatilememory in the first pixel circuit through a corresponding contactelectrode and a corresponding drive electrode of the first pixelcircuit.

The method can further include: forming a plurality of second lightemitting elements on a second substrate, each of the second lightemitting elements including second semiconductor layers epitaxiallygrown on the second substrate an being configured to emit light with asecond color different from the first color, the second semiconductorlayers including a second conductive outer layer on a side of the secondsemiconductor layers further from the second substrate; integrating thesecond light emitting elements formed on the second substrate with thebackplane device by bonding the second conductive outer layers of thesecond light emitting elements with conductive outer layers of secondpixel circuits in the plurality of pixel circuits, such that each of thesecond light emitting elements is bonded and conductively coupled to asecond pixel circuit that is adjacent to a corresponding first pixelcircuit in the backplane device; and then, after integrating the secondlight emitting elements, removing the second substrate from the secondlight emitting elements that remain integrated with the backplanedevice, where each of the second light emitting elements is adjacent toa corresponding first light emitting element on the backplane device.

A height of each of the second light emitting elements formed on thesecond substrate can be larger than or identical to a height of each ofthe first light emitting elements formed on the first substrate. Adistance between adjacent second light emitting elements on thebackplane device can be substantially identical to a distance betweenadjacent second pixel circuits in the backplane device, and a distancebetween adjacent first and second light emitting elements can be smallerthan or identical to a distance between adjacent pixel circuits in thebackplane device.

In some implementations, the method further includes: forming aplurality of third light emitting elements on a third substrate, each ofthe third light emitting elements including third semiconductor layersepitaxially grown on the third substrate and being configured to emitlight with a third color that is different from the first color and thesecond color, the third semiconductor layers including a thirdconductive outer layer on a side of the third semiconductor layersfurther from the third substrate; integrating the third light emittingelements formed on the third substrate with the backplane device bybonding the third conductive outer layers of the third light emittingelements with conductive outer layers of third pixel circuits in theplurality of pixel circuits, such that each of the third light emittingelements is bonded and conductively coupled to a third pixel circuitthat is adjacent to a corresponding first pixel circuit and acorresponding second pixel circuit in the backplane device; and then,after integrating the third light emitting elements, removing the thirdsubstrate from the third light emitting elements that remain integratedwith the backplane device, where each of the third light emittingelements on the backplane device is adjacent to a corresponding firstlight emitting element and a corresponding second light emitting elementon the backplane device.

A height of each of the third light emitting elements formed on thethird substrate can be larger than or identical to a height of each ofthe second light emitting elements formed on the second substrate thatcan be larger than or identical to a height of each of the first lightemitting elements formed on the first substrate.

In some implementations, the first light emitting elements areconductively connected to the first pixel circuits to form firstsub-pixels of active-matrix multi-color pixels, the second lightemitting elements are conductively connected to the second pixelcircuits to form second sub-pixels of the active-matrix multi-colorpixels, and the third light emitting elements are conductively connectedto the third pixel circuits to form third sub-pixels of theactive-matrix multi-color pixels. Each of the active-matrix multi-colorpixels can include a first sub-pixel having a first light emittingelement and a first pixel circuit, a second sub-pixel having a secondlight emitting element and a second pixel circuit, and a third sub-pixelhaving a third light emitting element and a third pixel circuit. Thefirst, second, and third light emitting elements in each of theactive-matrix multi-color pixels can be adjacent and conductivelyisolated from each other, and the respective first, second, and thirdpixel circuits can be adjacent and conductively isolated from eachother. Each of the active-matrix multi-color pixels includes a redlight-emitting diode (LED), a green LED, and a blue LED.

The method can further include: filling an isolation material in gapsbetween adjacent first, second and third light emitting elements thatremain integrated on the backplane device, where the isolation materialincludes an opaque and conductively isolated dielectric material. Eachof the first, second, third light emitting elements can include a firstcontact electrode as a conductive outer layer of the light emittingelement and a second contact electrode formed on a buffer layer that isformed on a corresponding substrate.

The method can further include: planarizing the first, second, thirdlight emitting elements with the isolation material filled in the gapsto remove the buffer layers to form a common surface with exposure ofthe second contact electrodes of the first, second, third light emittingelements. The method can further include: forming a transparentconductive layer on the common surface to form a common electrode forthe first, second, and third light emitting elements.

Another aspect of the present disclosure features an integrated deviceincluding: a backplane device including at least one backplane includinga plurality of pixel circuits that are conductively isolated from eachother; a plurality of first light emitting elements on first pixelcircuits in the plurality of pixel circuits, where each of the firstlight emitting elements includes one or more first light emitting layersbetween a first contact electrode and a second contact electrode andoperable to emit light with a first color, and where the first contactelectrode of each of the first light emitting elements is bonded andconductively coupled to a first pixel circuit in the backplane device; aplurality of second light emitting elements on second pixel circuits inthe plurality of pixel circuits, where each of the second light emittingelements includes one or more second light emitting layers between athird contact electrode and a fourth contact electrode and operable toemit light with a second color different from the first color, where thethird contact electrode of each of the second light emitting elements isbonded and conductively coupled to a second pixel circuit in thebackplane device, where surfaces of the second electrodes of the firstlight emitting elements are lower than surfaces of the fourth contactelectrodes of the second light emitting elements; and a transparentconductive layer on the plurality of first light-emitting elements andthe plurality of second light-emitting elements, where the transparentconductive layer is a common electrode in contact with the secondcontact electrodes of the first light-emitting elements and the fourthcontact electrodes of the second light-emitting elements.

The integrated device can further include: a plurality of third lightemitting elements on a plurality of third pixel circuits in thebackplane device, where each of the third light emitting elementsincludes one or more third light emitting layers between a fifth contactelectrode and a sixth contact electrode and operable to emit light witha third color different from the first color and the second color, andwhere the fifth contact electrode of each of the third light emittingelements is bonded and conductively coupled to a third pixel circuit inthe backplane device, and where the transparent conductive layer is incontact with the sixth contact electrodes of the third light-emittingelements.

In some implementations, the first light emitting elements areconductively connected to the plurality of first pixel circuits to formfirst sub-pixels of active-matrix multi-color pixels, the second lightemitting elements are conductively connected to the plurality of secondpixel circuits to form second sub-pixels of the active-matrixmulti-color pixels, the third light emitting elements are conductivelyconnected to the plurality of third pixel circuits to form thirdsub-pixels of the active-matrix multi-color pixels. Each of theactive-matrix multi-color pixels can include a first sub-pixel having afirst light emitting element and a first pixel circuit, a secondsub-pixel having a second light emitting element and a second pixelcircuit, and a third sub-pixel having a third light emitting element anda third pixel circuit. The first, second, and third light emittingelements in each of the active-matrix multi-color pixels can be adjacentand conductively isolated from each other, and the respective first,second, and third pixel circuits can be adjacent and conductivelyisolated from each other.

In some implementations, the first, second, and third light emittingelements are conductively isolated from each other by an opaquedielectric material. Surfaces of the sixth electrodes of the third lightemitting elements can be higher than the surfaces of the fourth contactelectrodes of the second light emitting elements. The second contactelectrodes of the first light emitting elements, the fourth contactelectrodes of the second light emitting elements, and the sixth contactelectrodes of the third light emitting elements, and the opaquedielectric material filled between the first, second, and third lightemitting elements can form a continuous and non-flat surface, and thetransparent conductive layer can be formed on the continuous andnon-flat surface.

The transparent conductive layer can be a continuous and non-flat layerformed on the surfaces of the second electrodes and the surfaces of thefourth contact electrodes.

A third aspect of the present disclosure features a method offabricating an integrated active-matrix multi-color pixel array baseddisplay, the method including: forming a plurality of light emittingelements on a semiconductor substrate, each of the light emittingelements includes multiple semiconductor layers epitaxially grown on thesemiconductor substrate and being configured to emit light with a firstcolor, the semiconductor layers including one or more quantum welllayers having Group III-V compounds between a first doped semiconductorlayer as a first contact electrode and a second doped semiconductorlayer as a second contact electrode; integrating the light emittingelements on the semiconductor substrate with a backplane device to forma plurality of active-matrix light emitting pixels by conductivelyconnecting the first contact electrode of each of the light emittingelements with a drive electrode of a respective pixel circuit in thebackplane device, where the backplane device includes at least onebackplane having a plurality of pixel circuits that are conductivelyisolated from each other, each of the pixel circuits including anon-volatile memory conductively coupled to the drive electrode of thepixel circuit, where each of the active-matrix pixels includes at leastone of the light emitting element and at least one of the non-volatilememories conductively coupled to the at least one of the light emittingelements, then removing the semiconductor substrate from the lightemitting elements that remain integrated on the backplane device; andforming an array of active-matrix multi-color display pixels byselectively depositing at least one phosphor film or quantum dots filmon at least one light emitting element in each of the active-matrixlight emitting pixels, the at least one phosphor film or quantum dotsfilm being operable to emit a secondary light when excited by the lightwith the first color from the at least one light emitting element, wherethe secondary light has a second color different from the first color.

The method can further include: after removing the semiconductorsubstrate from the light emitting elements, forming first isolationspacers between adjacent light emitting elements, the first isolationspacers including an opaque conductively isolated dielectric material;planarizing the light emitting elements with the first isolation spacersto expose the second contact electrodes of the light emitting elementsand to form a common surface across the second contact electrodes of thelight emitting elements; depositing a transparent conductive layer onthe common surface to form a common electrode for the light emittingelements integrated on the backplane device, where the at least onephosphor film or quantum dots film is selectively formed on thetransparent conductive layer; forming second isolation spacers betweenadjacent pixel elements of the active-matrix multi-color display pixelsand on the transparent conductive layer, the second isolation spacersincluding the opaque conductively isolated dielectric material; andforming a transparent protective layer on top of the active-matrixmulti-color display pixels and the second isolation spacers.

A fourth aspect of the present disclosure features an integrated deviceincluding: a backplane including a plurality of pixel circuits eachconductively coupled to respective light-emitting elements to form anarray of active-matrix light-emitting pixels, where each of thelight-emitting elements includes one or more quantum well semiconductorlayers between a first contact electrode and a second contact electrodeand is operable to emit light with a first color, each of the firstcontact electrodes of the light-emitting elements being respectively incontact with and conductively coupled to a drive electrode in arespective pixel circuit in the backplane; isolation spacers filledbetween adjacent light emitting elements, where the isolation spacersinclude an opaque dielectric material, and where surfaces of the secondcontact electrodes of the light emitting elements and surfaces of theisolation spacers form a common surface; a transparent conductive layeron the common surface, where the transparent conductive layer is acommon electrode in contact with the second contact electrodes of thelight-emitting elements; and for each of the active-matrix lightemitting pixels, at least one phosphor film or one quantum dot film onthe transparent conductive layer above at least one light emittingelement in the pixel and being operable to emit a secondary light whenexcited by the light with the first color from the at least onelight-emitting element, where the secondary light has a second colordifferent from the first color.

Drive electrodes of two adjacent pixel circuits in the backplane can beseparated by a dielectric spacer, and a size of an isolation spacerbetween adjacent light emitting elements respectively bonded on thedrive electrodes of the two adjacent pixel circuits can be smaller thanor identical to a size of the dielectric spacer.

Each of the active-matrix light emitting pixels can be configured to bean active-matrix multi-color display pixel including: a blue color lightemitting element operable to provide a blue color and at least two bluecolor light emitting elements with two different color phosphor films orquantum dot films operable to respectively emit a red color and a greencolor.

Particular embodiments of the subject matter described in thisspecification can be implemented so as to realize one or more of thefollowing advantages. Light emitting elements (e.g., LEDs) are firstformed on a first substrate (e.g., silicon or sapphire) and thenintegrated with a backplane (e.g., a CMOS backplane or a TFT arraycontrol backplane) formed on a second substrate (e.g., silicon, polymeror glass), e.g., by bonding. The light emitting elements can be alignedto be conductively coupled to respective pixel circuits in the backplaneto thereby form an array of active-matrix light emitting pixels (e.g.,LED pixels). After the integration, the first substrate can be removed,e.g., by laser peeling off, from the light emitting elements that remainintegrated on the backplane. Thus, this technology enables tosimultaneously integrate (or bond) a large number of light emittingelements on a backplane to form active-matrix light emitting pixels.Compared to individually transferring light emitting elements, aligningand bonding them on a backplane, this technology can greatly increasefabrication speed and fabrication accuracy. This technology also enablesto fabricate high density active-matrix light emitting pixels to achievehigh resolution displays and/or fabricate larger number of active-matrixlight emitting pixels to achieve large area displays.

In some implementations, this technology enables to form active-matrixmulti-color display pixels by sequentially integrating different colorlight emitting elements (e.g., blue color LEDs, green color LEDs, andred color LEDs) formed on different substrates on the same backplanewith removal of the different substrates for the light emitting elementsafter the integration. The different color light emitting elements canbe formed by patterning corresponding light emitting structures formedon the different substrates according to patterns of respective pixelcircuits on the backplane, such that the different color light emittingelements can be integrated with the respective pixel circuits on thebackplane. This technology enables to use commercial light emittingstructures formed on substrates (e.g., multiple semiconductor layersacross wafers) or arrays of light emitting elements formed onsubstrates, which can simplify manufacture costs and improve fabricationefficiency and quality.

In some implementations, this technology enables to form active-matrixmulti-color display pixels by first integrating single color LEDs (e.g.,blue color LEDs or UV LEDs) on substrates on a backplane to formactive-matrix light emitting pixels and then depositing different colorphosphor films or quantum dots (QDs) films on selected light-emittingelements to activate light with different colors. This technology alsoenables to use commercial light emitting elements formed on substrates(e.g., an array of LEDs on wafers), which can avoid dicing individualLEDs and simplify manufacture costs and improve fabrication efficiencyand quality.

Moreover, before the integration, the light emitting elements can beformed by high-quality deposition at high temperatures, e.g., byMetal-Organic Chemical Vapor Deposition (MOCVD), molecular beam epitaxy(MBE), atomic layer deposition (ALD), physical vapor deposition (PVD),Chemical Vapor Deposition (CVD), or any other deposition methods in avacuum chamber. The light emitting elements or corresponding lightemitting structures can be also commercially available. The CMOS/TFTbackplane can be fabricated by existing CMOS/TFT technologies, e.g., byan Original Equipment Manufacturer (OEM), which can greatly simplify themanufacture process.

For the integration, this technology enables to use low temperaturedirect bonding by pretreating surfaces of the light emitting elementsand/or surfaces of backplanes, e.g., with plasma activation. Thisbonding between the light emitting elements and the backplanes can befurther increased, secured or tightened by subsequent processes, e.g.,filling isolation spacers and surface planarization. In some cases, lowtemperature bonding with intermediate conductive layer, e.g., eutecticbonding, can be used. The bonding can produce hermetically sealedpackages and electrical interconnection within a single process and beconducted at low processing temperatures, low resultant stress inducedin final assembly, high bonding strength, large fabrication yield, and agood reliability.

Additionally, as drive electrodes in pixel circuits in the CMOS/TFTbackplane are formed with a predetermined mask during the CMOS/TFTmanufacturing process, the predetermined mask for the drive electrodescan be used for patterning a light emitting structure to form an arrayof light emitting elements, such that the light emitting elements can bealigned and bonded on respective drive electrodes (or pixel circuits) inthe backplane, thus enabling a high alignment accuracy.

The technology can use one or more quantum well layers of Group III-Vcompounds (e.g., GaN) as light emissive layers, which makes the LEDarrays more energy efficient and more stable than OLED (organic LED)based arrays. For example, the LEDs can be ultraviolet (UV) or deep UVcolor LEDs, blue color LEDs, green color LEDs or red color LEDs, bycontrolling the quantum well layers such as InGaN/GaN. The technologycan use different color LEDs to form multi-color displays. Thetechnology can also use phosphor materials or quantum-dot materialsdeposited on the III-V compound based LED arrays to produce multi-colordisplays. The technology can use isolation spacers to isolate conductiveconnection of adjacent LEDs and/or deposited phosphor materials orquantum dot materials on the adjacent LEDs. The isolation spacers caninclude an opaque dielectric material (e.g., SiNx) or a black materialand can be configured to block or eliminate light propagation betweenthe adjacent LEDs to thereby eliminate cross-talk between the adjacentLEDs. The technology can also integrate non-volatile memories, e.g.,SRAM (static random-access memory), with the LEDs to form active-matrixLED pixels, enabling higher efficiency and faster response time thanpassive-matrix LED pixels. The technology allows integratingnon-volatile memories and drivers on the CMOS/TFT backplane, whichgreatly simplifies processing, achieves seamless integration and reducescost. As the LEDs are made of semiconductor layers, additionalprotective layers are unnecessary to protect the LEDs from externalenvironments, unlike OLED or LCD displays. In some cases, atouch-sensitive protective film can be formed on surfaces of the LEDpixel arrays to form a capacitance sensitive screen.

In some implementations, the integrated LEDs and CMOS backplane onsemiconductor substrates enable the use of standard semiconductor IC(integrated circuit) manufacturing equipment, facilities, and processes,resulting in reduced cost. The integrated LED arrays on thesemiconductor substrate enables fabrication of an ultra-high resolutiondisplay, e.g., 100 μm per pixel, and/or micro-LED (μ-LED) displays withextremely high efficiency to save energy. The integrated LED pixelarray-based display systems, particularly micro-display systems, canachieve low power consumption (e.g., one order of magnitude lower thancurrent display devices), high resolution (e.g., 1080p), a thin devicethickness (e.g., no more than 1 mm), a large view angle (e.g., no lessthan 160 degrees), fast response time (e.g., ns), a high luminancecontrast modulation (e.g., 100%), and/or low cost due to integration.Particularly, the response time of the integrated LED systems can bethree orders of magnitude faster than that of OLED systems, and caneliminate flickering issues existing in OLED displays, whenpulse-width-modulation (PWM) technology is adopted. In someimplementations, CMOS backplanes based display systems can have a pixelsize less than 5.0 μm, a response time faster than 0.1 μs, and/or anemitting light flux higher than 20 cd/mm{circumflex over ( )}2. Thedisplay systems can have a thickness less than 1.0 mm, and/or a displayarea larger than 50 mm×50 mm. The display systems can be flexible.

The technology can use packaging techniques, e.g., conductive grid arraypackaging such as ball grid array (BGA) package, to form larger displayswith multiple integrated LED pixel array micro-displays (display modulesor panels), as described in a U.S. patent application Ser. No.15/396,135, entitled “LARGER DISPLAYS FORMED BY MULTIPLE INTEGRATED LEDARRAY MICRO-DISPLAYS” and filed on Dec. 30, 2016, whose content ishereby incorporated by reference in its entirety. On one hand, thelarger displays can still have the advantages of integrated LED pixelarray microarrays as noted above. On the other hand, this technology canovercome the current dimensional limit of displays fabricated by usingstandard silicon wafers. Using multiple LED pixel arrays basedmicro-displays to compose and assemble a larger micro-LED display, e.g.,active-matrix, enables an unlimited size display at a significantlylower cost. Moreover, the integrated LED pixel array micro-displays canform LEDs or LED pixels all over areas of the micro-displays, includingedges of the micro-displays, such that adjacent micro-displays havesubstantially no or little gap, e.g., less than 1 mm, which makes thelarger display a whole piece to seamlessly display a single image orvideo. In some cases, the illumination areas over the physical areas ofthe larger displays can be about 50% or more, e.g., 90%, substantiallylarger than those of LCD displays or OLED displays.

Compared to CMOS backplanes formed on a semiconductor wafer, TFTbackplanes can be formed on a larger substrate (e.g., glass) to form alarger display. Also TFT backplanes can be formed and connected on aflexible substrate (e.g., a polyimide film or a stainless steel) to forma flexible device. The TFT backplane can have a larger size than a CMOSbackplane formed on the semiconductor substrate. In someimplementations, TFT backplanes are formed on a larger substrate withoutBGA packaging that is used for connecting CMOS backplanes on differentsmaller substrates. In some implementations, TFT backplanes baseddisplay systems can have a pixel size less than 10 μm, a respond timefaster than 1.0 μs, and/or an emitting light flux higher than 10cd/mm{circumflex over ( )}2. The display systems can have a thicknessless than 1.0 mm, and/or a display area larger than 100 mm×100 mm. Thedisplay systems can be flexible, rollable, and foldable.

The TFT backplanes can be low-temperature polysilicon (LTPS)active-matrix (AM) TFT control backplanes. For example, LEDs formed onmultiple wafers (e.g., silicon or sapphire) can be aligned and bonded toTFT backplanes formed on a polyimide film that is formed on a carrierglass. The wafers for the LED structures can be removed, e.g., by laserlift-off. As noted above, active-matrix LED pixel arrays can be formedby sequentially bonding different color LEDs on the TFT backplanes or bydepositing different color phosphor materials or quantum-dot materialson single-color LEDs. After the integrated LED pixel arrays are formed,the carrier glass can be removed, e.g., by laser lift-off, to form aflexible device.

These integrated active-matrix multi-color LED pixel arrays baseddevices or systems can be widely used in many applications, includingportable electronic and communication devices, such as wearable devices(e.g., eyeglasses, watches, clothes, bracelets, rings), mobile devices,virtual reality (VR)/augmented reality (AR) displays, monitors,televisions (TVs), or any lighting or display applications.

The details of one or more disclosed implementations of the subjectmatter described in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages will become apparent from the description, the drawings andthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example integrated active-matrix LEDpixel array based display system, according to one or moreimplementations of the present disclosure.

FIGS. 2A-2B are schematic diagrams of example active-matrix LED pixels,according to one or more implementations of the present disclosure.

FIG. 2C shows an example timing diagram using active-matrix LED pixelsfor a video display, according to one or more implementations of thepresent disclosure.

FIG. 3A is a perspective view of an example integrated active-matrixmulti-color pixel array based display system using different color LEDsbonded on a backplane, according to one or more implementations of thepresent disclosure.

FIG. 3B is a cross-sectional view of the integrated display system ofFIG. 3A.

FIG. 3C is a top view of the integrated display system of FIG. 3A.

FIGS. 4A-1 and 4A-2 are perspective views of a multi-layered color LEDstructure formed on a substrate.

FIG. 4B-1 is a schematic diagram of an example multi-layered blue colorLED structure formed on a substrate.

FIG. 4B-2 is a schematic diagram of an example array of blue color LEDsformed by patterning the structure of FIG. 4B-1.

FIGS. 4B-3 and 4B-4 are schematic diagrams of example multi-layered bluecolor LED structures on a sapphire substrate (FIG. 4B-3) and on asilicon substrate (FIG. 4B-4), respectively.

FIG. 4C-1 is a schematic diagram of an example array of green color LEDsformed on a substrate.

FIG. 4C-2 is a schematic diagram of an example array of red color LEDsformed on a substrate.

FIGS. 4D-1 and 4D-2 show schematic diagrams of an example TFT arraybackplane device.

FIG. 4D-3 is a cross-sectional view of the TFT array backplane device ofFIGS. 4D-1 and 4D-2.

FIGS. 4E-1 and 4E-2 are schematic diagrams of an example process ofbonding multiple red color LED arrays on substrates onto a TFT arraybackplane device and removing the substrates.

FIG. 4F-1 is a schematic diagram of a bonded device including the redcolor LED arrays and the TFT array backplane device.

FIG. 4F-2 is a schematic diagram of a formed red color LED pixel of FIG.4F-1.

FIGS. 4G-1 and 4G-2 are schematic diagrams of an example process ofbonding multiple green color LED arrays on substrates onto a TFT arraybackplane device with integrated red color LED arrays and removing thesubstrates for the green color LED arrays.

FIG. 4H-1 is a schematic diagram of a bonded device including the redand green color LED arrays and the TFT array backplane device.

FIG. 4H-2 is a perspective view of the bonded device of FIG. 4H-1.

FIGS. 4I-1 and 4I-2 are schematic diagrams of an example process ofbonding multiple blue color LED arrays on substrates onto a TFT arraybackplane device with integrated red and green color LED arrays andremoving the substrates for the blue color LED arrays.

FIG. 4J-1 is a schematic diagram of a bonded device including the red,green and blue color LED arrays and the TFT array backplane device.

FIG. 4J-2 is a perspective view of the bonded device of FIG. 4J-1.

FIG. 4K is a schematic diagram of a device with dielectric spacersfilled in the bonded device of FIG. 4J-1.

FIG. 4L is a schematic diagram of a device including a transparentelectrode formed on a common surface of the bonded device of FIG. 4K.

FIG. 4M is a schematic diagram of a device including a transparentprotective layer and a polarizing film formed on the device of FIG. 4L.

FIG. 4N is a schematic diagram of an integrated device after removing acarrier glass from the device of FIG. 4M.

FIG. 5A is a perspective view of an example integrated display systemwith active-matrix multi-color LED pixel arrays fabricated by singlecolor LEDs bonded on a backplane with multiple color phosphors orquantum dot (QDs), according to one or more implementations of thepresent disclosure.

FIG. 5B is a cross-sectional view of the integrated display system ofFIG. 5A.

FIG. 6A is a schematic diagram of a multi-layered LED structure formedon a substrate.

FIG. 6B is a schematic diagram of an LED array formed by patterning thestructure of FIG. 6A.

FIGS. 6C and 6D are schematic diagrams of an example process of bondingmultiple LED arrays on substrates onto a TFT array backplane device andremoving the substrates for the LED arrays.

FIG. 6E is a schematic diagram of a bonded device including the LEDarrays and the TFT array backplane device.

FIG. 6F is a schematic diagram of a device with isolation spacers filledin the bonded device of FIG. 6E.

FIG. 6G is a schematic diagram of a device with a transparent electrodeformed on a common surface of the device of FIG. 6F.

FIG. 6H is a schematic diagram of a device with multiple color phosphorfilms formed on the device of FIG. 6G.

FIG. 6I is a schematic diagram of a flexible integrated device afterforming a protection layer and a polarizing film on the device of FIG.6H and removing the carrier glass of the TFT array backplane device.

FIG. 7 is a flow diagram of an example process of forming an integratedactive-matrix multi-color pixel display system by sequentially bondingdifferent color light emitting elements onto a backplane device.

FIG. 8 is a flow diagram of an example process of forming an integratedactive-matrix multi-color pixel display system by first bonding singlecolor light emitting elements onto a backplane device and thendepositing multiple color phosphors or QDs films.

DETAILED DESCRIPTIONS

The following descriptions are example display devices or systems thatinclude integrated active-matrix light-emitting diode (LED) pixel arrayson rigid substrates or flexible substrates. However, the disclosedimplementations can be adopted to any suitable system that needs formingintegration of two separate components, e.g., arrays of light-emittingelements and backplanes including integrated circuits, e.g.,non-volatile memories and/or drivers. For example, the substrates can bemade of any suitable material, e.g., rigid substrates such as silicon,silicon oxide, silicon carbide, gallium nitride, sapphire, glass, orspinel, or flexible substrates such as a polyimide film or a stainlesssteel. The light-emitting elements can include any suitable lightsources, e.g., semiconductor based LEDs, OLEDs, laser diodes, or laserssuch as vertical-cavity surface-emitting laser (VCSELs). The backplanecan be a CMOS backplane or a TFT array control backplane.

For illustration purposes only, in the following, FIG. 1 shows anexample integrated active-matrix LED pixel array based display system;FIGS. 2A-2B show example active-matrix LED pixels; FIG. 2C shows anexample timing diagram using active-matrix LED pixels for a videodisplay; FIGS. 3A-3C show an example integrated active-matrixmulti-color pixel array based display system by bonding three differentcolor LED arrays on a backplane device; FIGS. 4A-1 to 4N show an exampleprocess of fabricating a display system of FIGS. 3A-3C; FIGS. 5A-5B showan example integrated active-matrix multi-color pixel array baseddisplay system by bonding single color LED arrays on a backplane deviceand forming different color phosphors or QDs on the LEDs;

FIGS. 6A to 6K show an example process of fabricating a display systemof FIGS. 5A-5B; FIG. 7 is an example process of fabricating anintegrated display system of FIGS. 3A-3C; and FIG. 8 is an exampleprocess of fabricating an integrated display system of FIGS. 5A-5B.

Example Display System

FIG. 1 is a schematic diagram of an example integrated active-matrix LEDpixel array based display system 100, according to one or moreimplementations of the present disclosure. The display system 100 can bea display module including LED pixel arrays and display drivers such asscanning drivers and data drivers. The display system 100 can be coupledto a control system, e.g., via a wired or wireless connection. Thecontrol system can control the display system 100 to operate to displayimages/videos.

In some implementations, the control system includes one or moreprocessors and/or controllers, e.g., a central processing unit (CPU), amicrocontroller unit (MCU), and/or integrated circuits (ICs), e.g.,sensors, analog/digital converters (ADCs), digital/analog converters(DACs), amplifiers, drivers, and/or timers. The control system can alsoinclude a memory, e.g., a read-only memory (ROM) and/or a random-accessmemory (RAM). The processors and/or controllers can be coupled to thememory via connections, e.g., internal bus, conductive electrodes, wiredconnections, or wireless connections. The processors and/or controllersare configured to read data from or store data into the memory. Forexample, the processors and/or controllers can receive image or videodata to be displayed, e.g., from external network or devices, processthe image or video data, and/or store the processed image or video datain the memory. The memory can also store instructions to cause theprocessors and/or controllers to execute operations. Components of thecontrol system can be monolithically manufactured on a semiconductorsubstrate.

In some implementations, the control system includes one or more digitalsignal processors including: a digital signal analyzer, a digitalprocessor, an image processor, a volatile memory, a non-volatile memory,and/or a touch screen processor. The control system can also include oneor more analog signal processors including a light signal sensor, anelectrical signal sensor, a sound signal sensor, a sound signalprocessor, an analog signal amplifier, an ADC, a DAC, a touch screensignal processor, and/or any other associated electronic components. Theanalog signal processors are connected to and communicate with thedigital signal processors through an ADC and/or a DAC. In operation, theanalog signal processors can receive and process image or video signalsfrom external devices or network or from the internal memory. The imageor video signals may be analog signals which can be processed andconverted into digital signals by an ADC. The digital signals arefurther processed and analyzed by the digital signal processors. Thenthe processed digital data can be further transmitted from the digitalsignal processors to particular data drivers and scanning drivers whichthen select particular LEDs and control the selected LEDs for display.

The display system 100 includes an active-matrix LED pixel array 118, adata driver 114 and a scanning driver 116. As illustrated in FIG. 1, theLED pixel array 118 is composed of 640 (columns)×480 (rows) pixel matrixarranged in columns and rows, respectively. Each pixel 120 is anactive-matrix LED pixel. As illustrated in FIGS. 2A-2B below, anactive-matrix LED pixel includes at least one LED and at least onenon-volatile memory coupled to the at least one LED. Upon receiving thedata instructions from the scanning driver 116 and/or the data driver114, the non-voltage memory can enable each pixel to operatecontinuously and independently without waiting for the next instructioncoming after a full scan.

The number of LEDs in the LED pixel array 118 is equal to n times of thenumber of pixels, where n is an integer. If each pixel includes one LED,n is 1; if each pixel includes two LEDs, n is 2; if each pixel includesthree LEDs, n is 3; if each pixel includes four LEDs, n is 4.

In some examples, an LED pixel includes a plurality of LEDs, e.g., blue,red, and green color LEDs, and a plurality of corresponding non-volatilememories. Each LED is coupled to a respective non-volatile memory. Insome examples, the LED pixel includes a white LED. In some examples, theLED pixel includes four LEDs including three LEDs emitting basic lightsuch as red, blue, and green, and a white LED emitting white light. Insome examples, one non-volatile memory is coupled to one LED. In someexample, one non-volatile memory is coupled to two or more LEDs emittingthe same color, and the two or more LEDs can be in two or more differentpixels.

In some implementations, the scanning driver 116 includes 480displacement storages 125, 480 relay drivers 126, and 480 pulse widthmodulators 127. Each row of LED pixels is coupled to a respectivedisplacement storage 125, a respective relay driver 126, and arespective pulse width modulator 127 through a respective word line (orscanning line) 117. The scanning driver 116 can receive instructionsfrom the control system, e.g., the processors/controllers, and selectone or more particular LED pixels based on those instructions.

In some implementations, the data driver 114 is divided into twosub-drivers positioned on top and bottom of the array 118 of LED pixels,respectively. Each sub-driver can be a 320×4-bit data driver and include54 section displacement storage 121, 54×6×4-bit storages 122 and 123,and/or 320 digital-to-analog converters (DACs) 124. Each sub-driver iscoupled to 320 columns of LED pixels through respective column bitlines. Particularly, the top sub-driver is coupled to 320 columns of LEDpixels through odd column bit lines, and the bottom sub-driver iscoupled to another 320 columns of LED pixels through even column bitlines. An intersection of an individual bit line 115 and an individualword line 117 is coupled to a respective LED pixel. That is, selectingthe individual bit line 115 and the individual word line 117 canuniquely select the respective LED pixel. The sub-data drivers canreceive instructions and/or data from the control system, e.g., theprocessors/controllers, and select one or more particular LED pixelswith the scanning driver 116 based on the instructions and/or data andtransmit data to the selected particular LED pixels through respectivebit lines 115.

In some implementations, the active-matrix LED pixel array 118 iscovered by a protective layer. The protective layer can be transparent.In some examples, the protective layer is made of glass coated with aconductive material like indium tin oxide (ITO). The protective layerdefines an array of spots corresponding to the array of LEDs. Each spotcovers an LED underneath and is coupled to a corresponding non-volatilememory coupled to the LED. The spot and the surface of the LED may forma capacitor, and/or one or more additional capacitors may be formedbetween the spot and the LED. When the spot is touched, e.g., by afingertip on top of the spot or moving towards the spot, a capacitanceof the capacitors can change. The capacitance change can be detected bya touch screen detector/processor in the control system through thenon-volatile memory and a corresponding data driver 114/scanning driver116 coupled to the non-volatile memory. Thus, the protective layer, theLED array, and the corresponding non-volatile memories can form a touchscreen position sensor, which, together with the touch screendetector/processor in the control system, enables the LED pixel displaysystem 100 to function as a touch screen display. Additionalimplementations of the touch screen sensor on the LEDs are alsopossible, e.g., using other technologies like resistive sensing, surfaceacoustic wave, infrared grid, infrared acrylic projection acoustic pulserecognition, or dispersive signal technology.

In some implementations, as discussed in further details below, thedisplay system 100 is formed by integrating an array of LEDs formed on afirst substrate and a backplane device formed on a second substrate andthen removing the first substrate from the LEDs that remain bonded onthe backplane device. The data drivers, the scanning drivers, thenon-volatile memories, and the connection lines including the bit linesand the word lines can be integrated in the backplane device. Each ofthe LEDs can be conductively coupled to a respective non-volatile memoryin the backplane device to form an active-matrix LED pixel. In someimplementations, different color LED arrays can be sequentiallyintegrated on the backplane device to form active-matrix multi-color LEDpixels. In some implementations, single color LED arrays can beintegrated on the backplane device and then different color phosphormaterials or quantum dots materials can be selectively deposited onsurfaces of the LEDs to form active-matrix multi-color display pixels.The backplane device can be configured to drive, e.g., transmit displaydata to, the active-matrix multi-color display pixels bypulse-width-modulation (PWM) technology. Due to fast response time(e.g., nanoseconds) of the LEDs, flickering issues can be eliminated andthe display system 100 can be flicker free.

Example Active Matrix LED Pixels

FIG. 2A shows an example active-matrix LED pixel 200 with non-volatilememory. The LED pixel 200 includes an S-RAM (static-random accessmemory) 202 and an LED 204. The S-RAM 202 includes a driver transistor(T1) 212, a switching transistor (T2) 214, and a storage capacitor (Cs)216. During display operation, a word line (scanning line or selectline) can be pulled high to allow a voltage on a bit line to propagatethrough the switching transistor 214 to a storage node 205, charging thestorage capacitor 216 and setting a high voltage on a gate of the drivertransistor 212. This allows a current to pass through the drivertransistor 212 and the LED 204 is consequently lighted.

FIG. 2B shows another example active-matrix LED pixel 230 withnon-volatile memory 232 and an LED 234. The non-volatile memory 232includes a driver transistor 242 and a switching transistor 244, thatcan be thin-film transistors (TFTs). In some implementations, differentfrom the LED pixel 200 in FIG. 2A, the brightness of the LED 234 is notcontrolled by varying VData applied to a gate of the driver transistor242 through the switching transistor 244. Instead, a constant VData isapplied to the gate of the driver transistor 242. The current throughthe driver transistor that causes the LED 234 to illuminate iscontrolled by changing a threshold voltage VT of the driver transistor242, e.g., through programming. If low brightness is desired, the drivertransistor 242 can be set to a high threshold voltage by programmingwith a large positive gate pulse. If high brightness is desired, thedriver transistor 242 can be set to a low threshold voltage byprogramming with a small positive gate pulse, or not programming at all,the leaving it with the initial threshold voltage. Thus, an image orvideo can be displayed by controlling the brightness or on/off status ofthe LEDs of an array.

FIG. 2C shows an example video scan timing 250 of a display using theactive-matrix LED pixel 230 of FIG. 2B. After programming (i.e.,programming mode), the display is activated by setting a supply voltageVDD to 10 V, VData to 8 V on all the bit lines, and Vsdect to 10 V onall the word lines (select lines). The LED current and thereforebrightness of the pixel 230 is determined by the programmed thresholdvoltage of the driver transistor 242. Both VData and Vsdect are DCvoltages in the display mode because a pixel refresh is not necessary tomaintain a static image. The image information remains stored in thethreshold voltage of the driver transistor 242 even if the power isturned off. To change the programmed image, the pixels can be firsterased and then reprogrammed. Erase mode in FIG. 2C is identical to theprogram operation. The only difference is that the applied voltage pulsehas a larger negative amplitude, instead of a positive one. Thisnegative voltage forces the trapped electrons in the driver transistor242 to tunnel back out, causing the threshold voltage to shift towardsits original un-programmed value. For example, to erase a single pixelin the active matrix (instead of an entire column), all other selectlines can be held at −30 V to prevent the erase pulse from propagatingto the undesired pixel drivers.

Example Systems and Fabricating Processes Using Multiple Color LEDArrays

FIGS. 3A-3C show an example integrated display system 300 using threedifferent color LED arrays and a backplane device. The integrateddisplay system 300 can be the display system 100 of FIG. 1. Thisintegrated display system 300 can be formed according to an exampleprocess described with further details in FIGS. 4A-1 to 4N.

As illustrated in FIGS. 3A-3C, the integrated display system 300includes a backplane 310 on a first side of a substrate 302. In someimplementations, the backplane 310 can be a CMOS backplane formed in aCMOS backplane device. The CMOS backplane device can include one or moreCMOS backplanes and can be manufactured by existing CMOS manufacturingtechnologies. The substrate 302 can be a silicon substrate, e.g., asilicon wafer. In some implementations, the backplane 310 can be a TFTarray control backplane formed in a TFT backplane device. The TFTbackplane device can include one or more TFT backplanes and can bemanufactured by existing TFT manufacturing technologies, e.g., by OEMs.The TFT array backplane can be a low temperature polysilicon (LTPS)thin-film transistors (TFT) array control backplane.

The backplane 310 includes integrated circuits having non-volatilememories and display drivers 312. In some implementations, the backplane310 includes a number of pixel circuits. Each pixel circuit includes anon-volatile memory that has at least one transistor conductivelycoupled to a corresponding drive electrode 314 in a top layer of thepixel circuits or a top layer of the backplane 310. Adjacent driveelectrodes 314 are conductively isolated from each other by dielectricspacers 316. The display drivers include scanning drivers and datadrivers, and each of the non-volatile memories is coupled to one of thescanning drivers through at least one word line and to one of the datadrivers through at least one bit line.

The integrated display system 300 includes arrays of light-emittingelements such as LEDs 330. The LEDs 330 are separated (or isolated) byisolation spacers 340, e.g., dielectric spacers. The isolation spacers340 are configured to isolate the LEDs 330 such that the LEDs 330 arenot conductively connected. The isolation spacers 340 can include anopaque dielectric material or a dielectric material with alight-absorbing material such as a black material, such that light froman LED is blocked or eliminated from propagating to an adjacent LED andthus there is no or little cross-talk between the adjacent LEDs. Theopaque dielectric material can include silicon nitride (SiNx). SiNx hasa hexagonal crystal structure at an ambient pressure and sinteredceramic of this phase is opaque. Each LED 330 can include a firstcontact electrode such as p-electrode 334 (e.g., p-GaN layer), a secondcontact electrode such as n-electrode 336 (e.g., n-GaN layer), andmultiple quantum well (MQW) semiconductor layers 332 between thep-electrode 334 and the n-electrode 336. The MQW layers 332 can includegroup III-V nitrides (e.g., GaN) and each of the LEDs 330 is operable toemit light with a single color, e.g., blue, green, or red.

The emitted wavelength of an LED is dependent on the MQW materials' bandgap and can be controlled by a thickness of InGaN layer (e.g., in arange of 2-3 nm) and GaN/InN ratio, from near ultraviolet (UV) for0.02In/0.98Ga through 390 nm for 0.1In/0.9Ga, violet-blue 420 nm for0.2In/0.8Ga, blue 440 nm for 0.3In/0.7Ga, green 532 nm for 0.5In/0.5Ga,to red for higher ratios In/Ga.

The LEDs 330 include three different color LED arrays: blue color LEDs330 a, green color LEDs 330 b, and red color LEDs 330 c. Each blue colorLED 330 a is operable to emit light with a blue color, and the MQWlayers can include multiple pairs of In(0.3)Ga(0.7)N/GaN layers. Eachgreen color LED 330 b is operable to emit light with a green color, andthe MQW layers can include multiple pairs of In(0.5)Ga(0.5)N/GaN layers.Each red color LED 330 c is operable to emit light with a red color, andthe MQW layers can include multiple pairs of InN/GaN layers. In somecases, a display pixel can include one blue color LED 330 a, one greencolor LED 330 b, and one red color LED 330 c. In some cases, a displaypixel can include three blue color LEDs 330 a, three green color LEDs330 b, and three red color LEDs 330 c that can be arranged as a squareor rectangular unit. The arrays of blue color LEDs 330 a, green colorLEDs 330 b, and red color LEDs 330 c can be periodically arranged on thebackplane 310.

FIG. 3C shows an example arrangement of the three LED arrays, whereadjacent single color LEDs are separated by two other color LEDs along arow and same color LEDs are arranged along a column. Other arrangementsof different color LED arrays are also possible, which can be determinedbased on a design of display pixels.

Each LED 330, e.g., blue color LED 330 a, green color LED 330 b, or redcolor LED 330 c, is coupled to a respective pixel circuit that includesa non-volatile memory in the backplane 310 by conductively connectingthe p-electrode 324 to a drive electrode 314 of the pixel circuit. Insuch a way, the array of LEDs 320 is coupled to respective pixelcircuits in the backplane 310 to form an array of active-matrix LEDpixels. As discussed with further details below, the p-electrode 324 andthe drive electrode 314 can be bonded together. The bonding techniquecan include, but is not limited to: direct bonding such as lowtemperature direct bonding with or without an intermediate conductivelayer, fusion bonding, diffusion bonding, eutectic bonding with anintermediate conductive layer, and/or transient liquid phase bonding.The direct bonding can be plasma assisted, e.g., by using plasma toactivate one or more to-be-bonded surfaces before bonding.

In an active-matrix LED pixel, a non-volatile memory includes at leastone transistor. The transistor has a drain node made of metal material,which is conductively connected to the drive electrode 314 throughconductive via, e.g., made of metal material. The drive electrode 314can have a larger area than the drain node of the transistor. The driveelectrode 314 can be also made of metal material, e.g., indium tin oxide(ITO). Thus, in the pixel, the non-volatile memory is conductivelyconnected to an LED through multiple metal contacts including the drainnode, the conductive via, and the drive electrode 314.

Each LED 330 can be aligned with the respective drive electrode 314. Insome cases, the LED 330 has a smaller area size than the drive electrode314 and within an area of the drive electrode 314. In some cases, theLED 330 has a same area size as the drive electrode 314 and can beoverlapped on the area of the drive electrode 314. In some cases, theLED 330 has a larger area size than the drive electrode 314 but smallerthan the drive electrode 314 and adjacent dielectric spacer 316, suchthat the LED 330 can have a larger area (for a higher pixel fillingcoefficient) but be conductively isolated from each other.

A transparent conductive layer 350, e.g., an indium tin oxide (ITO)layer, is on top of the arrays of LEDs 330. The transparent conductivelayer 350 is in contact with the n-electrodes 326 of the LEDs 330 toform a common transparent electrode of the LEDs 330. As the LEDs 330 aremade of semiconductor materials, in some examples, there is no anadditional protective layer added on top of the LEDs 330.

In some implementations, a transparent protective layer is deposited ontop of the transparent conductive layer 350. The protective layer can bea touch-sensitive transparent layer and can form, together with thetransparent conductive layer 350 (as the common electrode), a capacitivetouch screen position sensor.

In some cases, a polarizing film can be deposited between thetransparent conductive layer 350 and the transparent protective layer.The polarizing film can be configured to allow light from the LEDs 330to propagate through along a polarization direction to become apolarized light.

In some implementations, an intermediate conductive layer, e.g., a metallayer, can be formed on top of each LED, e.g., on a contact electrodesuch as p-GaN electrode 334. The intermediate conductive layer can havea smoother surface than that of the contact electrode, which canincrease adhesion between the LED and the backplane during directbonding. A surface of the intermediate conductive layer can be plasmaactivated before bonding. In some cases, the intermediate conductivelayer can be used for low temperature eutectic bonding or fusionbonding. In some cases, each of the intermediate conductive layers canform a highly-reflective mirror for a corresponding LED 330 bonded withthe intermediate conductive layer. The mirror can have a reflectivityhigher than 80% for the wavelengths of light emitted by the LED 330. Theintermediate conductive layer can have a same area size as thecorresponding LED 330. The contact electrode p-GaN 334 can include ametal film with a high reflectivity and can be configured to enhance abrightness of light emitted from the LED 330. Each of the active-matrixlight-emitting pixels is operable to output a light flux in onedirection that is larger than 80% of light flux in two directions outputfrom each of the at least one LED 330 in the pixel.

Referring now to FIGS. 4A-1 to 4N, steps of fabricating a displaysystem, e.g., the display system 300 of FIGS. 3A-3C, are illustrated.For illustration purposes only, in the following, a TFT control arraybackplane device is used for fabricating the display system.

FIGS. 4A-1 and 4A-2 show an LED device 400 (e.g., an LED wafer) having amulti-layered LED structure 402 formed on a substrate 401 (e.g., awafer). The substrate 401 can be pre-treated, e.g., by cleaning a topsurface of the substrate 401. Then the multi-layered LED structure 402is formed by directly depositing (e.g., epitaxially growing) multiplelayers on the top surface of the substrate 401. The multiple layers caninclude a buffer (and/or sacrificial) layer, a first contact electrode,light-emitting layers, and a second contact electrode that aresequentially formed on the substrate 401. The multiple layers can bedeposited by Metal-Organic Chemical Vapor Deposition (MOCVD), molecularbeam epitaxy (MBE), atomic layer deposition (ALD), physical vapordeposition (PVD), Chemical Vapor Deposition (CVD), or any other suitabledeposition methods in a vacuum chamber with a certain temperature. Thelight-emitting layers can include one or more quantum well layers ofgroup III-V compounds for emitting light with a specified color. Notethat LED structures formed on substrates can be commercially prepared,e.g., through OEM.

FIG. 4B-1 is a schematic diagram of an example multi-layered blue colorLED structure 400 formed on the substrate 411. The substrate 411 can bea sapphire substrate, a silicon substrate, or a silicon carbide (SiC)substrate. The blue color LED structure 400 can include a buffer layer403 (e.g., AlGaN layer and GaN layer), an n-electrode layer 404 (e.g.,n-GaN layer) as a first contact electrode, MQW layers 405, and ap-electrode layer 406 (e.g., p-GaN layer) as a second contact electrodethat are sequentially formed on the substrate 401.

FIG. 4B-2 is a schematic diagram of a structure 410 including an arrayof blue color LEDs 412 formed after patterning the blue color LEDstructure 400 of FIG. 4B-1. Each of the blue color LEDs 412 can beoperable to emit light with a wavelength of about 460 nm.

The patterning can be performed according to different designs orconfigurations. For example, in an integrated device such as theintegrated device 300 of FIG. 3C, adjacent same color LEDs are separatedby two other different color LEDs along rows and same color LEDs arealong columns. That is, along each row, two adjacent blue color LEDs areseparated by a green color LED and a red color LED; two adjacent greencolor LEDs are separated by a red color LED and a blue color LED; andtwo adjacent red color LEDs are separated by a blue color LED and agreen color LED. Each LED is bonded with a corresponding drive electrodeof a respective pixel circuit in a backplane. Thus, patterning the bluecolor LED structure 400 can be based on a pattern of the correspondingdrive electrodes of pixel circuits for the blue color LEDs 412. Adjacentdrive electrodes are separated by one dielectric spacer, while adistance between adjacent blue color LEDs 412 within a row issubstantially identical to a distance between corresponding pixelcircuits for the blue color LEDs 412 in the backplane, that is, abouttwo drive electrodes and dielectric spacers between the drive electrodesand the blue color LEDs.

A protective mask can be obtained based on information for fabricatingthe drive electrodes in the backplane. For example, the drive electrodesare fabricated by forming a protective mask (e.g., photoresist or hardmask), depositing materials of the drive electrodes, and removing theprotective mask layer. The pattern of the protective mask for patterningthe LED structure 400 can be determined based on the protective mask forfabricating the drive electrodes, but with different spacings for LEDs,such that the LED structure 400 can be selectively etched away duringthe patterning. The patterning can be performed with the followingsteps: 1) patterning a hard mask layer, e.g., SiNx such as Si₃N₄, on topof the LED structure 400, e.g., on the p-electrode layer 406 (e.g.,p-GaN) of the LED structure 400; 2) etching through the layers of theLED structure 400, to the substrate 411; 3) removing the remaining hardmask layer.

As illustrated in FIG. 4B-2, the LED structure 400 is patterned to forman array of blue color LEDs 412. Adjacent blue color LEDs 412 areseparated from each other by spaces reserved for other color LEDs. Insome cases, the formed blue color LED 412 has a smaller area size than adrive electrode of the backplane and within an area of the driveelectrode. In some cases, a formed LED 412 has a same area size as thedrive electrode and can be overlapped on the area of the driveelectrode. In some cases, a formed LED 412 has a larger area size thanthe drive electrode but smaller than the drive electrode and adjacentdielectric spacer, such that the LED 412 can have a larger area but beconductively isolated from each other.

FIG. 4B-3 shows an example III-V blue color LED 412 a formed on asapphire substrate 411 a. The III-V blue light LED 412 a includesmultiple sequentially grown epitaxial layers, including a buffer layer413 a, e.g., 4.5 μm-GaN layer, a n-type contact electrode 414 a, e.g., 1μm n doped GaN layer, MQW 415 a, e.g., 30 pairs of 1.2 nm-InGaN/4.5nm-GaN layers, and a p-type contact electrode, e.g., 150-nm p doped GaNlayer, that are directly formed on a surface of the sapphire substrate411 a.

FIG. 4B-4 shows an example III-V blue color LED 412 b formed on asilicon substrate 411 b. The silicon substrate 411 b can be a silicon(111) substrate, where a surface of the silicon substrate can beparallel to a (111) crystalline plane. The III-V blue light LED 412 b isformed on the silicon substrate 411 b by using alternating pairs of anInGaN layer and a GaN:Si layer as the quantum well (MQW) layers 415 b.The LED 412 b can include one or more buffer layers 413 b deposited onthe silicon substrate 411 b, one or more lower Group III-V compoundlayers 414 b as a first contact electrode on the buffer layers 413 b,MQW layers 415 b on the lower Group III-V compound layers 414 b, and oneor more upper Group III-V compound layers 416 b as a second contactelectrode.

In a particular example, the blue light LED 412 b includes sequentiallyepitaxially grown layers with MOCVD (or MBE or ALD): 30 nm-AlN layerunder 700° C., 50 nm-AlN layer under 1200° C., 200 nm-AlGaN layer under1200° C., 500 nm-GaN layer under 1200° C., 10 nm-AlN layer under 600°C., 50 nm-AlN layer under 1200° C., 400 nm-AlGaN layer under 1200° C.,1.5 μm-GaN:Si layer under 1200° C., 5 pairs of 5-nm InGaN layer and 10nm-GaN:Si layer under 800° C., 10 nm-AlGaN:Mg layer under 1200° C., and300 nm-GaN:Mg layer under 1200° C.

FIG. 4C-1 shows an example 420 of an array of green color LEDs 422fabricated on a substrate 421. The substrate 421 can be c-plane sapphirewafer, m-plane GaN wafer, silicon wafer, or SiC wafer. A III-V greencolor LED structure can be first formed on the substrate 421 andpatterned to form the green color LEDs 422. The patterning can beperformed according to a pattern of corresponding pixel circuits in abackplane. Similar to the array of blue color LEDs 412, two adjacentgreen color LEDs 422 within a row are separated by the space needed fortwo corresponding pixel circuits and dielectric spacers.

The III-V green color LED 422 can include sequentially grown epitaxiallayers, including a buffer layer 423, e.g., GaN/AlGaN layer, a n-typecontact electrode 426, e.g., n doped GaN layer, MQW layers 427, e.g.,InGaN/GaN layers, and a p-type contact electrode, e.g., p doped GaNlayer, on the substrate 421. In a particular example, the green colorLED 422 can include 20˜40 nm AlGaN layer, 3 to 4.5 μm GaN layer, 1.5 to3 μm n-GaN contact electrode layer, 250 nm to 400 nm MQW layers, and 100to 250 nm p-GaN contact electrode layer, on a c-plane sapphire wafer ora m-plane GaN wafer. Each of the III-V green color LEDs 420 can beoperable to emit light with a wavelength of about 520 nm.

FIG. 4C-2 shows an example red color LED device 430 including an arrayof red color LEDs 432 fabricated on a substrate 431. The substrate 431can be transparent GaP (or InGaP) wafer or opaque GaAs wafer. A III-Vred color LED structure can be first formed on the substrate 431 andthen patterned to form the array of red color LEDs 432. The patterningcan be performed according to a pattern of corresponding pixel circuitsin a backplane. Similar to the array of blue color LEDs 412, twoadjacent red color LEDs 432 within a row are separated by the space needfor two corresponding pixel circuits and dielectric spacers.

The III-V red color LED 432 can include multiple sequentially grownepitaxial layers including a buffer layer 433 (or a sacrificial lightabsorption epitaxy layer), a n-type contact electrode 434, e.g., n dopedInGaP layer, MQW layers 435, e.g., InN/GaN layers, AlGaAs or InAlGaPlayers, and a p-type contact electrode 436, e.g., p doped InGaP layer.The sacrificial layer can be made of InGaAsN or AlGaInP material. In aparticular example, the red color LED 432 can include an AlGaInPsacrificial layer of 300˜400 nm, a n-GaN contact electrode layer of 50nm to 100 nm, a n-AlGaInP current spreading layer of 2 μm to 4 μm, MQWlayers of 400 nm to 500 nm, and a p-GaP contact electrode layer of 2.5μm to 3.2 μm, on a GaAs wafer. The III-V red color LED 432 can beoperable to emit light with a wavelength of about 650 nm.

FIGS. 4D-1 to 4D-3 show schematic diagrams of an example TFT arraybackplane device 440. The TFT array backplane device 440 can befabricated on a polyimide film 444 on a carrier glass 442, usingstandard TFT manufacturing processes, e.g., by OEMs. The TFT backplanedevice 440 can include one or more TFT backplanes 450 on top of thepolyimide film 444.

Each TFT backplane 450 can include one or more polysilicon layers 452and integrated circuits (including a number of non-volatile memories anddrivers 454) formed on the polysilicon layers 452. The drivers includescanning drivers, e.g., the scanning drivers 116 of FIG. 1, and datadrivers, e.g., the data drivers 114 of FIG. 1. Each non-volatile memoryis coupled to one of the scanning drivers through at least one wordline, e.g., the word line 117 of FIG. 1, and to one of the data driversthrough at least one bit line, e.g., the bit line 115 of FIG. 1. Eachnon-volatile memory includes at least one transistor coupled to arespective drive electrode 456 on top of the TFT backplane 450. Adjacentdrive electrodes 456 are isolated from each other by dielectric spacers458.

FIG. 4D-3 is an expanded cross-sectional view of the TFT backplanedevice 440. Each non-volatile memory includes at least one transistor454 a. The transistor 454 a has drain 454 b, gate 454 c, and source 454d, which are separated by dielectrics 454 e. The transistor 454 a iscoupled to a respective drive electrode 456 in a top layer of the TFTbackplane 450 through metal via 459. Via 451 can be formed betweenadjacent transistors 454 a. A shadow mask 453 is formed on top of thetransistor 454 a. Then a metal shield 457 is formed on the shadow mask453. An interlayer 455 including dielectric material is formed betweenthe metal shield 457 and the drive electrodes 456 for isolation.

Multiple implementations can be realized to integrate LED arrays on abackplane device. The bonding techniques can include but not limited to:direct bonding such as low temperature direct bonding with or without anintermediate conductive layer, fusion bonding, diffusion bonding,eutectic bonding with an intermediate conductive layer, and transientliquid phase bonding.

In some implementations, the LED array can be bonded onto the backplanedevice using low temperature bonding, e.g., eutectic bonding. Anintermediate conductive layer can be deposited on top of an LEDstructure, e.g., the blue color LED structure 400 of FIG. 4B-1, formedon a substrate, and then the LED structure and the intermediateconductive layer can be patterned together to form an array of LEDs withan intermediate conductive sub-layer on top of each LED. Accordingly,the intermediate conductive sub-layer has a same area size as acorresponding LED underneath. The intermediate conductive layer caninclude one or more intermediate metallic layers, for example, aniridium-tin-oxide (ITO) film with a titanium (Ti) film, a cupper (Cu)film with a Tantalum (Ta) film, an aluminum (Al) film with a Tin (Sn)film, and/or a gold (Au) or silver (Ag) film with at least one adhesivefilm including chromium (Cr), Platinum (Pt), Palladium (Pd), or Titanium(Ti).

In some implementations, an LED array can be directly bonded onto thebackplane device, e.g., by pretreating at least one of surfaces of theLEDs or a surface of the backplane device, for example, with plasmaactivation. For illustration purposes only, direct bonding between anLED device including LEDs formed on a substrate and a backplane deviceis described in the following steps.

To achieve good bonding, one or two bonding surfaces can be pre-treatedto remove any contamination and/or oxide film that can hamper adhesionof the bonding surfaces. The bonding surfaces can be pre-treated to besmooth and uniform. In some examples, the pre-treatment includes: I)treating the bonding surfaces by a 10 min piranha (H₂O₂:H₂SO₄=1:3 byvolume) solution pre-clean followed by deionized water rinse andspin-dry prior to metallization; II) treating the bonding surfaces withan ultraviolet (UV)-ozone pre-clean to remove the organic surfacecontamination; and III) before bonding, applying a low energy plasmaactivation of the bonding surfaces of the LED device and the backplanedevice.

A direct bonding process can be described as follows: first, both theLED device and the backplane device are placed in a vacuum chamber withpressures, e.g., near 1×10{circumflex over ( )}−3 Torr, or in anatmosphere pressure nitrogen (N2) environment; second, the LED device isflipped over with the LEDs' contact electrodes facing to a top layer ofthe backplane device, aligned and clamped together on a bonding chuck;third, a pressure, e.g., 30 psi, is applied on both sides of the bondeddevices when the devices are in a full contact at a predeterminedtemperature, e.g., 300° C., for a predetermined period, e.g., 1 hour.Optionally, the bonded devices can be further annealed with atemperature, e.g., near 400° C., for an additional predetermined timeperiod, e.g., about 1 hour.

The LED device can be aligned to the backplane device for bonding by,for example, optically aligning marks on an LED substrate with marks onthe backplane device, such that each LED is aligned to a correspondingpixel circuit of the backplane device, and a contact electrode of theLED is aligned to a drive electrode of the corresponding pixel circuitin the top layer of the backplane device.

After the bonding, the substrate of the LED device can be removed fromthe LEDs that remain bonded with the backplane device, that is, theconduct electrodes of the LEDs are bonded with the corresponding driveelectrodes (or pixel circuits) of the backplane device. The removing ofthe LED substrate can be performed by a peeling-off process, a lift-offprocess, a splitting process, a detaching process, or a laser scribingprocess. Techniques of ion implantation, laser annealing, thermalannealing, and mechanical clipping can be used individually or incombination to weaken interfaces of the separation. For illustrationpurposes only, in the following, laser lift-off is described forremoving substrates of LED devices.

The backplane device can have a large area and multiple same color LEDdevices are to be bonded onto the whole area of the backplane device.The same color LED devices can be sequentially bonded onto differentareas of the backplane device followed with removal of their LEDsubstrates, such that a previous bonded LED device will not obstruct afollowing LED device to be bonded onto the backplane device. In someimplementations, a step and scan lift-off method can be adopted. Afteran LED device is bonded to the backplane device, a laser scanning andlift-off process is performed on an area, e.g., a rectangular area, ofthe LED device, so that the LEDs in the area scanned by the laser areseparated from the LED substrate and remain bonded to the backplanedevice. The LEDs in the non-scanned area of the LED device remain withthe LED substrate and can be moved away (or lifted off) from thebackplane device. Thus, an array of LEDs is bonded on the backplanedevice. The LED substrate can be cleaned and reused.

As discussed with further details below, different color LED devices,e.g., blue color LED devices 410, green color LED devices 420, and redcolor LED devices 430, can be sequentially bonded with a backplanedevice. The bonding sequence of the different color LED devices can bein any desired order. For example, it can be a sequence of blue, green,and red, a sequence of blue, red, and green, a sequence of red, green,and blue, a sequence of red, blue, and green, a sequence of green, red,and blue, or a sequence of green, blue, and red. For illustrationpurposes only, the sequence of red, green, and blue is described in thefollowing.

FIGS. 4E-1 and 4E-2 are schematic diagrams of an example process ofbonding multiple red color LED device 430 onto a TFT array backplanedevice 440 and removing LED substrates after the bonding. The TFT arraybackplane device 440 includes at least one TFT array control backplane450 including a plurality of pixel circuits. Each of the pixel circuitsincludes a drive electrode 456 in the top layer of the backplane 450.Each red color LED device 430 includes an array of LEDs 432 formed on anLED substrate 431. Each red color LED 432 can have a height H1, from thesacrificial layer 433 to a top p-InGaP contact electrode 436. Adjacentred color LEDs 432 are separated to reserve a space for a blue color LEDand a green color LED.

As noted above, the multiple red color LED devices 430 are bonded ontothe TFT array backplane device 440. As illustrated in FIG. 4E-1, a firstred color LED device 430 is flipped over with the p-electrode 436 facingto drive electrodes 456 of pixel circuits of the TFT backplane 450. Thefirst red color LED device 430 is aligned, e.g., by optically aligningmarks, and bonded on drive electrodes 456 in a first area of thebackplane device 440, e.g., by low temperature direct bonding asdescribed above. Then, as illustrated in FIG. 4E-2, the substrate 431 ofthe first red color LED device 430 is removed, e.g., by laser lift-off,from the red color LEDs 432 that remain bonded on a first area of thebackplane device 440, and then a second red color LED device 430 isaligned and bonded onto a second area of the backplane device 440, thesecond area being adjacent to the first area.

In some cases, the red color LEDs 432 is formed on a GaP substrate 431,which can be delaminated by UV Excimer Laser (with a wavelength at 248nm or 308 nm) lift-off. The epitaxial layer-selective delamination isachieved by photochemical decomposition of the sacrificial layer 433,e.g., an intermediate opaque layer, next to the transparent GaPsubstrate 431. The GaP substrate 431 can be cleaned and reused.

In some cases, the red color LEDs 432 is formed on a GaAs substrate 431.The GaAs substrate can be delaminated by Nd:YAG Laser (with a wavelengthof 1064 nm) lift-off. The epitaxial layer of InGaAsN can be used as anintermediate sacrificial layer for selective photodecomposition andsubstrates lift off. By tuning the composition of the InGaAsN layer suchthat its bandgap is lower than 1.165 eV (energy of a 1064 nm photon),the InGaAsN layer strongly absorbs 1064 nm laser light to which the GaAssubstrate is effectively transparent. Upon absorption of the laserpulse, ablation occurs along the InGaAsN layer, separating the GaAs filmfrom its GaAs growth substrate, producing a crack-free GaAs layeradhered to a flexible polymer substrate. In a particular example, aQ-switched Nd:YAG laser with a pulse duration (full width at halfmaximum—FWHM) of 8-9 ns, GaAs substrate wafer lift-off is achieved overa large range of average fluences from ˜0.6 J/cm{circumflex over ( )}2to ˜3.5 J/cm{circumflex over ( )}2. In some cases, the GaAs substrate431 can be also delaminated by Chemical Lift-Offs (CLO). Since GaAs isopaque, an intermediate sacrificial layer of AlAs or InAlP can be grownon the GaAs substrates before AlGaAs or InAlGaP multiple quantum wells.By selective etching AlAs intermediate sacrificial layers using HF, theGaAs substrate can be lifted off and by selective etching InAlPintermediate sacrificial layers using HCl, the GaAs substrate can belifted off. The GaAs substrate can be cleaned and reused.

In some implementations, one or more red color LED devices 430 can befirst bonded onto the TFT backplane device 440 and then be removed theLED substrates 431 together. For example, the red color LED devices 430can have a rectangular (or square) shape and can be bonded onto thebackplane device 440 without or with little gaps therebetween. Then theLED substrates 431 can be laser lift-offs or chemical lift-offs.

FIGS. 4F-1 and 4F-2 show a bonded device 460 obtained by bondingmultiple red color LED devices 430 onto the TFT array backplane device440 and then removing the LED substrates 431 from the red color LEDs 432that remain (or are left) bonded on the drive electrode. The remainingred color LED 432 has a height H1′. As the laser lift-off of the LEDsubstrate 431 can remove part of the sacrificial layer 433, the heightH1′ of the remaining red color LED 432 is smaller than the height H1 ofthe original red color LED 432. Two adjacent red color LEDs 432 along arow are separated by a space reserved for two other color LEDs, and thespace has a distance of two driver electrodes 456 and dielectric spacers458 therebetween.

Similarly, as discussed with further details below, green color LEDarrays and blue color LED arrays can be sequentially bonded onto thebackplane device 440.

FIGS. 4G-1 and 4G-2 are schematic diagrams of an example process ofbonding multiple green color LED arrays formed on substrates onto thebonded device 460 and removing the LED substrates after the bonding. Thebonded device 460 includes the TFT array backplane device 440 withintegrated arrays of red color LEDs 432, and the adjacent red color LEDs432 are separated by two drive electrodes 456 and dielectric spacers 458therebetween.

Multiple green color LED devices 420 are bonded onto the bonded device460. Each green color LED device 420 includes an array of LEDs 422formed on an LED substrate 421. Adjacent green color LEDs 422 areseparated to reserve a space for a blue color LED and a red color LED.Each green color LED 422 can have a height H2, from the buffer layer 423to the top p-GaN contact electrode 426. The height H2 of the green colorLED 422 needs to be larger than the height H1′ of the remaining redcolor LED 432 on the TFT backplane 450, such that the green color LEDdevice 420 touch the surface of the TFT backplane 450 without movementof the substrate 421 being obstructed by the red color LEDs 432 that arealready bonded on the TFT backplane 450. As the height H1′ may vary overa range and be not known, the height H2 can be configured to beidentical to or higher than the height H1 of the original red color LEDs432 formed on the LED substrate 431. As the height H1 is larger than theheight H1′, the height H2 of the original green color LED 422 formed onthe LED substrate 422 is larger than the height H1′. In someimplementations, the buffer layer 423 of the green color LED 422 can beconfigured to have a larger thickness than the buffer layer 433 of thered color LED 422, such that the height H2 is higher than the height H1.

As illustrated in FIG. 4G-1, a first green color LED device 420 isflipped over with the p-electrode 426 facing to drive electrodes 456 ofpixel circuits of the TFT backplane 450. The first green color LEDdevice 420 is aligned, e.g., by optically aligning marks, and bonded ondrive electrodes 456 in a first area of the bonded device 460, e.g., bylow temperature direct bonding as described above. The green color LEDs422 can be bonded to drive electrodes 456 adjacent to red color LEDs 432bonded on the TFT backplane 450.

After the bonding, as illustrated in FIG. 4G-2, the substrate 421 of thefirst green color LED device 420 is removed from the green color LEDs422 that remain bonded on the first area of the bonded device 460. Thena second green color LED device 420 is aligned and bonded onto a secondarea of the bonded device 460, the second area being adjacent to thefirst area. As illustrated in FIG. 4G-2, as the height H2 is larger thanthe height H1′, the top p-electrodes 426 of the green color LEDs 422formed on the second green color LED device 420 can contact with thecorresponding drive electrodes 456 in the top layer of the TFT backplane450, without obstruction of the red color LEDs 432 bonded in the secondarea of the bonded device 460.

The substrate 421 of the green color LED device 420 can be removed by ascan and lift-off process with a laser. In some examples, the substrate421 is a sapphire substrate. Since sapphire is transparent and GaN (thematerial of the buffer layer 423) is opaque (which absorbs light), a GaNfilm can be lifted off from the sapphire substrate by a short pulse KrFUV excimer laser with a wavelength of 248 nm or 308 nm, e.g., in a powerrange of 0.4-0.8 J/cm². The sapphire substrate 421 can be cleaned andreused.

In some implementations, one or more green color LED devices 420 can befirst bonded onto the bonded device 460 and then be removed from the LEDsubstrates 421 together. For example, the green color LED devices 410can have a rectangular (or square) shape and can be bonded onto thebonded device 460 without or with little gaps therebetween. Then the LEDsubstrates 421 can be lifted off by a short pulse laser.

FIGS. 4H-1 and 4H-2 show a bonded device 470 obtained by bondingmultiple green color LED devices 420 onto the bonded device 460(including red color LEDs 432 bonded on TFT array backplane device 450)and then removing the LED substrates 421 from the green color LEDs 422that remain bonded on the TFT array backplane 450. The remaining greencolor LED 422 has a height H2′. As the laser lift-off of the LEDsubstrate 421 can remove part of the buffer layer 423, the height H2′ ofthe remaining green color LED 422 is smaller than the height H2 of theoriginal green color LED 422. Two adjacent green color LEDs 422 along arow are separated by a bonded red color LED 432 and a space reserved fora blue color LED, and the space has a distance of one driver electrode456 and dielectric spacers 458 therebetween.

FIGS. 4I-1 and 4I-2 are schematic diagrams of an example process ofbonding multiple blue color LED arrays on LED substrates onto the bondeddevice 470 and removing the LED substrates after the bonding. The bondeddevice 470 includes the TFT array backplane device 440 with integratedarrays of red color LEDs 432 and arrays of green color LEDs 422. Thebonded device 470 includes spaces reserved for blue color LEDs andseparated by a green color LED 422 and a red color LED 432.

Multiple blue color LED devices 410 are bonded onto the bonded device470. Each blue color LED device 410 includes an array of blue color LEDs412 formed on a LED substrate 411. Adjacent blue color LEDs 412 areseparated to reserve a space for a green color LED and a red color LED.Each blue color LED 412 can have a height H3, from the buffer layer 413to the top p-GaN contact electrode 416. The height H3 of the green colorLED 422 needs to be larger than the height H1′ of the remaining redcolor LED 432 and the height H2′ of the remaining green color LED 422 onthe TFT backplane 450, such that the blue color LED device 410 can touchthe surfaces of TFT backplane 450 without movement of the substrate 411being obstructed by the red color LEDs 432 and the green color LEDs 422that are already bonded on the TFT backplane 450. As the height H2′ mayvary over a range and be not available, the height H3 can be configuredto be identical to or larger than the height H2 of the original greencolor LEDs 422 formed on the LED substrate 421. As the height H2 islarger than the height H2′ and larger than the height H1, the height H3of the original green color LED 422 formed on the LED substrate 422 islarger than the heights H2′ and H1′. In some implementations, thethickness of the buffer layer 413 of the blue color LED 412 isconfigured to be larger than the thickness of the buffer layer 423 ofthe green color LED 422 and the thickness of the buffer layer 433 of thered color LED 432, such that the height H3 is larger than the height H1and the height H2.

As illustrated in FIG. 4I-1, a first blue color LED device 410 isflipped over with the p-electrode 416 facing to drive electrodes 456 ofpixel circuits of the TFT backplane 450. The first blue color LED device410 is aligned, e.g., by optically aligning marks, and bonded on driveelectrodes 456 in a first area of the bonded device 470, e.g., by lowtemperature direct bonding as described above. The blue color LEDs 412can be bonded to drive electrodes 456 between red color LEDs 432 andgreen color LEDs 422 that remain bonded on the TFT backplane 450.

After the bonding, as illustrated in FIG. 4I-2, the substrate 411 of thefirst blue color LED device 410 is removed from the blue color LEDs 412that remain bonded on the first area of the bonded device 470. Then asecond blue color LED device 410 is aligned and bonded onto a secondarea of the bonded device 470, the second area being adjacent to thefirst area. As illustrated in FIG. 4I-2, as the height H3 is larger thanthe heights H1′ and H2′, the top p-electrodes 416 of the blue color LEDs412 formed on the second blue color LED device 410 can contact with thecorresponding drive electrodes 456 in the top layer of the TFT backplane450, without the obstruction of the red color LEDs 432 and the greencolor LEDs 422 that remain bonded in the second area of the bondeddevice 470.

The substrate 411 of each blue color LED device 410 can be removed by ascan and lift-off process with a laser. In some examples, the substrate411 is a sapphire substrate. Since sapphire is transparent and GaN (thematerial of the buffer layer 413) is opaque (which absorbs light), a GaNfilm can be lifted off from the sapphire substrate by a short pulse KrFUV excimer laser with a wavelength of 248 nm or 308 nm, e.g., in a powerrange of 0.4-0.8 J/cm². The short pulse laser is absorbed by the GaNfilm to generate a high temperature, e.g., more than 1000° C. Even abrief heating of an interface between the sapphire substrate and the GaNfilm to >1000° C. can result in decomposition of GaN into Ga, a lowmelting-point metal, and nitrogen which remains trapped at theinterface. The sapphire substrate can be cleaned and reused.

In some implementations, one or more blue color LED devices 410 can befirst bonded onto the bonded device 470 and then be removed the LEDsubstrates 411 together. For example, the blue color LED devices 410 canhave a rectangular (or square) shape and can be bonded onto the bondeddevice 470 without or with little gaps therebetween. In some examples,the LED substrate 411 is a silicon substrate, e.g., a silicon wafer. TheLED substrates 411 of the bonded blue color LED devices can be removedby chemical wet etching or Chemical Lift-Offs (CLO).

FIGS. 4J-1 and 4J-2 show a bonded device 480 obtained by bondingmultiple blue color LED devices 410 onto the bonded device 470(including arrays of red color LEDs 432 and arrays of green color LEDs422 bonded on TFT array backplane device 440) and then removing the LEDsubstrates 411 from the blue color LEDs 412 that remain bonded on theTFT array backplane device 440, together with the red color LEDs 432 andthe green color LEDs 422. The remaining blue color LED 412 has a heightH3′. As the laser lift-off of the LED substrate 411 can remove part ofthe buffer layer 413, the height H3′ of the remaining blue color LED 412is smaller than the height H3 of the original blue color LED 412. Insome implementations, the height H3 is higher than the height H2 that ishigher than the height H1, and the height H3′ is also higher than theheight H2′ that is higher than the height H1′. That is, in the bondeddevice 480, the blue color LEDs 412 can have a higher height than thegreen color LEDs 422 that are higher than the red color LEDs 432.

In the bonded device 480, adjacent LEDs are separated by gaps and areconductively isolated by dielectric spacers 458 in the gaps. On onehand, to increase a pixel filling coefficient that is defined as a ratiobetween a light-emitting area in a single pixel and a pixel physicalsurface area, the gaps between adjacent LEDs should be minimized. On theother hand, the adjacent LEDs should be conductively isolated from eachother. The adjacent LEDs are bonded on drive electrodes 456 ofrespective pixel circuits that are conductively isolated by dielectricspacers 458. Thus, a size of an LED (in both row and column) can beconfigured to be larger than a size of a drive electrode 456 but smallerthan a size of a drive electrode 456 and a dielectric spacer 458.

FIG. 4K is a schematic diagram of a device 482 with isolation spacers483 filled in the bonded device 480 of FIG. 4J-1. After the bondeddevice 480 is formed, a conductively isolated material can be depositedto fill into gaps between adjacent LEDs in the bonded device 480 to formthe isolation spacers 483. The isolated material can be an opaquedielectric material or a dielectric material with a light-absorbingmaterial such as a black material, such that light from an LED isblocked or eliminated from propagating to an adjacent LED and thus thereis no or little cross-talk between the adjacent LEDs. The opaquedielectric material can include silicon nitride (SiNx). SiNx has ahexagonal crystal structure at an ambient pressure and sintered ceramicof this phase is opaque. SiNx can be deposited in the gaps by chemicalvapor deposition (CVD).

Then, topology planarization is performed to remove the buffer layers ofthe LEDs to form a common surface 484 with exposure of n-contactelectrodes of the LEDs, e.g., n-InGaP electrodes 434 of red color LEDs432, n-GaN electrodes 424 of green color LEDs 422, and n-GaN electrodes414 of blue color LEDs 412. The common surface 484 is a surface afterthe topology planarization and can be flat or non-flat.

For TFT backplane device formed on the carrier glass 422, an etch-backplanarization can be carried out by isotropic inductive-coupled plasmaetching to remove the isolation material and the epitaxial buffer layersor sacrificial layers to expose the n-contact electrodes (e.g., n-GaNlayers or n-InGaP layers). The isotropic inductive-coupled plasmaetching can be reactive-ion etching with inert gases, such as Argon orxenon. In some cases, etch-back can be further used for thinning then-contact electrodes by etching a portion of the n-contact electrodes.In some cases, as noted above, in the bonded device 480, the blue colorLEDs 412 can have a higher height than the green color LEDs 422 that arehigher than the red color LEDs 432. After the etch-back process,surfaces of the n-GaN electrodes 414 of the blue color LEDs 412 may behigher than surfaces of the n-GaN electrodes 424 of the green color LEDs422 that are higher than surfaces of the n-InGaP electrodes 434 of thered color LEDs 432. That is, the surfaces of the n-contact electrodesand the surfaces of isolation spacers 483 therebetween form a continuousand non-flat surface.

In some implementations, a CMOS backplane device is used. After themultiple color LEDs are integrated on the CMOS backplane device andisolation spacers are filled into gaps between adjacent LEDs, a CMP(Chemical-Mechanical-Polishing) planarization can be carried out toremove the isolation material and the epitaxial buffer layers andsacrificial layers to expose n-contact electrodes of the LEDs. The CMPplanarization can form a continuous and flat surface across then-contact electrodes of the LEDs and the isolation spacers therebetween.The CMP process can be further used for thinning the n-contactelectrodes of the LEDs by removing a portion of the n-contactelectrodes. In some cases, an etch-back planarization can be carried outon the CMOS backplane device, and the etch-back planarization can form acontinuous and non-flat surface across the n-contact electrodes of theLEDs and the isolation spacers therebetween.

FIG. 4L is a schematic diagram of a device 486 including a transparentconductive layer (or a transparent electrode) 485 formed on the commonsurface 484 of the device 482 of FIG. 4K. The transparent conductivelayer 485, e.g., an ITO layer, is deposited on top of the common surface484 including the surfaces of the n-contact electrodes of the LEDs 412,422, and 432 to form a common electrode, e.g., an electrical commonground.

FIG. 4M is a schematic diagram of a device 490 including a transparentprotective layer 488 and a polarizing film 487 formed on the device 486of FIG. 4L. The polarizer film 487 can be deposited on the transparentconductive layer 485. The polarizer film 687 is configured to allowlight from the LEDs to propagate through along a polarization directionto become a polarized light, which can also reduce scattering and getmore uniform light. The transparent protective layer 488 can be thenformed on the polarizer film 487. The transparent protective layer 488can be a touch-sensitive transparent layer and can form, together withthe transparent conductive layer 485, a capacitive touch screen positionsensor. The transparent protective layer 488 can be made of transparentmaterial, e.g., glass or plastic, coated with a conductive material,e.g., indium tin oxide (ITO).

FIG. 4N shows a schematic diagram of a device 492 after removing thecarrier glass 422 from the device 490 of FIG. 4M. The integrated device490 has the polyimide film 444 on the carrier glass 442 as thesubstrate. To form a flexible device, the carrier glass 442 can beremoved from the integrated device 490, e.g., by laser lift-off. Forexample, the polyimide-coated carrier glass 442 can be delaminated viaUV excimer laser lift-off, e.g., at 308 nm, with an ablation threshold,e.g., at 235 mJ/cm{circumflex over ( )}2.

Example Systems and Fabricating Processes Using Single Color LED Arraysand Multiple Color Phosphor or Quantum Dots (QDs) Materials

FIGS. 5A and 5B show an example integrated display system 500 withactive-matrix multi-color LED pixel arrays fabricated by single colorLEDs 520 bonded on a backplane 510 with multiple color phosphor orquantum dots (QDs) materials, according to one or more implementationsof the present disclosure. The integrated display system 500 can be thedisplay system 100 of FIG. 1. This integrated display system 500 can beformed according to steps described with further details in FIGS. 6A to6I.

As illustrated in FIGS. 5A-5B, the integrated display system 500includes a backplane 510 on a first side of a substrate 502. In someimplementations, the backplane 510 can be a CMOS backplane formed in aCMOS backplane device. The CMOS backplane device can include one or moreCMOS backplanes and can be manufactured by existing CMOS manufacturingtechnologies. The substrate 502 can be a silicon substrate, e.g., asilicon wafer. In some implementations, the backplane 510 can be a TFTarray control backplane formed in a TFT backplane device. The TFTbackplane device can include one or more TFT backplanes and can bemanufactured by existing TFT manufacturing technologies, e.g., by OEMs.The TFT array backplane can be a low temperature polysilicon (LTPS)thin-film transistors (TFT) array control backplane.

The backplane 510 includes integrated circuits having non-volatilememories and display drivers 512. In some implementations, the backplane510 includes a number of pixel circuits. Each pixel circuit includes anon-volatile memory that has at least one transistor conductivelycoupled to a corresponding drive electrode 514 in a top layer of thepixel circuits or a top layer of the backplane 510. Adjacent driveelectrodes 514 are conductively isolated from each other by dielectricspacers 516. The display drivers include scanning drivers and datadrivers, and each of the non-volatile memories is coupled to one of thescanning drivers through at least one word line and to one of the datadrivers through at least one bit line.

The integrated display system 500 includes an array of light-emittingelements such as LEDs 520. The LEDs 520 are separated (or isolated) byisolation spacers 528. The isolation spacers 528 can include an opaquedielectric material or a dielectric material with a light-absorbingmaterial such as a black material, such that light from an LED isblocked or eliminated from propagating to an adjacent LED and thus thereis no or little cross-talk between the adjacent LEDs. The opaquedielectric material can include silicon nitride (SiNx).

Each LED 520 can include a first contact electrode p-electrode 524,e.g., p-GaN layer, a second contact electrode n-electrode 526, e.g.,n-GaN layer, and multiple quantum well (MQW) semiconductor layers 522between the p-electrode 524 and the n-electrode 526. The MQW layers 522can include group III-V compounds and each of the LEDs 520 is operableto emit light with a single color.

In some implementations, the LEDs 520 are blue color LEDs operable toemit light with a blue color. The MQW layers can include multiple pairsof In(0.3)Ga(0.7)N/GaN layers. In some other implementations, the LEDscan be a UV or deep UV LED. The MQW layers can include multiple pairs ofAlGaN/GaN layers. In some other implementations, the LEDs can be greencolor LEDs operable to emit light with a green color. The MQW layers caninclude multiple pairs of In(0.5)Ga(0.5)N/GaN layers. In some otherimplementations, the LEDs can be red color LEDs operable to emit lightwith a red color. The MQW layers can include multiple pairs of InN/GaNlayers.

Each LED 520 is coupled to a respective pixel circuit, e.g., anon-volatile memory, in the backplane 510 by conductively connecting thep-electrode 524 to a drive electrode 514 of the pixel circuit. In such away, the array of LEDs 520 is coupled to respective pixel circuits inthe backplane 510 to form an array of active-matrix LED pixels 534. Asdiscussed above, the bonding technique can include but not limited to:direct bonding such as low temperature direct bonding with or without anintermediate conductive layer, fusion bonding, diffusion bonding,eutectic bonding with an intermediate conductive layer, and/or transientliquid phase bonding. The direct bonding can be plasma assisted, e.g.,by using plasma to activate one or more to-be-bonded surfaces beforebonding.

Each LED 520 can be aligned, e.g., by optical alignment of marks, withthe respective drive electrode 514. In some cases, the LED 520 has asmaller area size than the drive electrode 514 and within an area of thedrive electrode 514. In some cases, the LED 520 has a same area size asthe drive electrode 514 and can be overlapped on the area of the driveelectrode 514. In some cases, the LED 520 has a larger area size thanthe drive electrode 514 but smaller than the drive electrode 514 andadjacent dielectric spacer 516, such that the LED 520 can have a largerarea (for a higher pixel filling coefficient) but be conductivelyisolated from each other, e.g., by isolation spacers 528. On one hand,to increase a pixel filling coefficient, gaps between adjacent LEDs 520should be minimized. On the other hand, the adjacent LEDs 520 should beconductively isolated from each other and have no light cross-talk. Theadjacent LEDs 520 are bonded on drive electrodes 514 of respective pixelcircuits that are conductively isolated by dielectric spacers 516. Thus,a size of an LED 520 (in both row and column) can be configured to belarger than a size of a drive electrode 516 but smaller than a sum of asize of the drive electrode 514 and a size of a dielectric spacer 516.

A transparent conductive layer 530, e.g., an indium tin oxide (ITO)layer, is on top of the array of LEDs 520. The transparent conductivelayer 530 is in contact with the n-electrodes 526 of the LEDs 520 toform a common electrode of the LEDs 520.

A phosphor material or a quantum dot material can be deposited on thetransparent conductive layer 530 above at least one LED 520 and operableto emit a secondary light when excited by the light emitted from the LED520. The secondary light can have a secondary color different from asingle color from the LED 520. As illustrated in FIGS. 5A-5B, red colorquantum dot (QD) materials or phosphor materials 534 a, green colorQDs/phosphors 534 b, and yellow color QDs/phosphors 534 c can bedeposited on the blue color LEDs 520 and operable to emit light withred, green, and white colors, respectively.

As an example, the LED 520 is a blue color LED, and each LED pixel 534in FIGS. 5A-5B includes a blue color LED sub-pixel with a transparentlayer or blue QDs or phosphors 534 d on a blue color LED 520, a redcolor LED sub-pixel with the red QDs/phosphor 534 a on a blue color LED520, a green color LED sub-pixel with green QDs/phosphors 534 b on ablue color LED 320, and a white LED sub-pixel with yellow QDs/phosphors534 c on a blue color LED 520. Each sub-pixel includes a non-volatilememory in the backplane 510 coupled to the blue color LED 520 via thedrive electrode 514 and the p-electrode 524. The red QDs/phosphors 534a, green QDs/phosphors 534 b, yellow QDs/phosphors 534 c, andtransparent layers (or blue QDs/phosphors) 534 d are isolated from eachother by opaque dielectric spacers 532, e.g., SiNx. The four LEDsub-pixels can be arranged in a rectangular shape or a square shape.Each LED sub-pixel can have a size of about 30 μm or less. Each LEDpixel can have a size of about 100 μm or less. In some implementations,a ratio between an area of light emission from the pixels and a physicalarea of the pixels is higher than 50%. In some other implementations,each LED pixel can also include three LED sub-pixels including a bluecolor LED sub-pixel, a red color LED sub-pixel, and a green color LEDsub-pixel.

In the system 500, a number of the LEDs 520 is larger than a number ofthe LEDs covered with the phosphor materials or quantum dots materials,and the number of the LEDs 520 is equal to at least two times of anumber of the LED pixels 534. For example, each LED is operable as alight-emitting diode (LED) to emit light with a blue color, e.g., with awavelength between 450 nm and 500 nm, and, for each of the active-matrixlight emitting pixels, at least two blue color LEDs are configured tooptically excite at least two other colors, e.g., green and red, bysecondary light emission of the phosphor materials or quantum dotsmaterials on the at least two blue color LEDs. Thus, each of theactive-matrix light emitting pixels is configured to be a multi-colordisplay pixel including one blue color LED operable to provide a bluecolor and the at least two blue color LEDs with the phosphor materialsor quantum dots materials operable to respectively provide a red colorand a green color.

In some other implementations, each of the LEDs is operable as a UV ordeep UV LED operable to emit light with a wavelength between 100 nm and450 nm, and, for each of the active-matrix light emitting pixels, atleast three UV or deep UV LEDs are configured to optically excite atleast three colors, e.g., red, green, and blue, by secondary lightemission of the phosphor materials or quantum dots materials on the atleast three UV or deep UV LEDs. The pixel can also include a UV or deepUV LED deposited with yellow color phosphor materials or quantum dotsmaterials to emit a white color.

Differences between different light conversion efficiencies amongdifferent pixel elements in each display pixel can be compensated bycontrolling pixel area ratios among the different pixel elements in thedisplay pixel, or controlling different drive currents for the differentpixel elements in the display pixel, or both. For example, the pixelareas ratios among the different pixel elements can be designed for alarger compensation, and the drive currents for the different pixelelements can be designed for a smaller compensation, e.g., for finetuning.

A polarizer film 536 can be deposited on surfaces of the pixels 534 andthe opaque dielectric spacers 532. The polarizer film 536 is configuredto allow light from the pixels 534 to propagate through along apolarization direction to become a polarized light.

A protective layer 538 can be formed on the polarizer film 536. Theprotective layer can be a touch-sensitive transparent layer and canform, together with the transparent conducive layer 530 (as the commonelectrode), a capacitive touch screen position sensor.

In some implementations, an intermediate conductive layer, e.g., a metallayer, can be formed on top of each LED, e.g., on a contact electrodesuch as p-GaN electrode. The intermediate conductive layer can have asmoother surface than that of the contact electrode, which enables toincrease adhesion between the LED and the backplane during directbonding. A surface of the intermediate conductive layer can be plasmaactivated before bonding. In some cases, the intermediate conductivelayer can be used for low temperature eutectic bonding or fusionbonding. In some cases, each of the intermediate conductive layers canform a highly-reflective mirror for a corresponding LED bonded with theintermediate conductive layer. The mirror can have a reflectivity higherthan 80%. The intermediate conductive layer can have a same area size asthe corresponding LED. The contact electrode p-GaN can include a metalfilm with a high reflectivity and can be configured to enhance abrightness of light emitted from the LED. Each of the active-matrixlight-emitting pixels is operable to output a light flux in onedirection that is larger than 80% of light flux in two directions outputfrom each of the at least one LED in the pixel.

Referring now to FIGS. 6A to 6I, steps of fabricating an integrateddisplay system, e.g., the display system 500 of FIGS. 5A-5B, areillustrated. For illustration purposes only, a TFT control arraybackplane device and blue color LEDs are used for fabricating theintegrated display system.

FIG. 6A shows a blue color LED device 600 (e.g., an LED wafer) having amulti-layered blue color LED structure 602 formed on a substrate 601(e.g., a wafer). The substrate 601 can be a sapphire substrate, asilicon substrate, or a silicon carbide (SiC) substrate. The substrate601 can be pre-treated, e.g., by cleaning a top surface of the substrate601. Then the multi-layered blue color LED structure 602 is formed bydepositing multiple layers on the top surface of the substrate 601. Themultiple layers can include a buffer layer 603, a first contactelectrode, e.g., n-GaN electrode 604, light-emitting layers, e.g., MQW605, and a second contact electrode, e.g., p-GaN electrode 606, that aresequentially formed on the substrate 601. The multiple layers can bedeposited (or epitaxially grown) by Metal-Organic Chemical VaporDeposition (MOCVD), molecular beam epitaxy (MBE), atomic layerdeposition (ALD), physical vapor deposition (PVD), Chemical VaporDeposition (CVD), or any other suitable deposition methods in a vacuumchamber with a certain temperature.

FIG. 6B is a schematic diagram of a structure 610 including an array ofblue color LEDs 612 formed by patterning the blue color LED structure600 of FIG. 6A. Each of the blue color LEDs 612 can be operable to emitlight with a wavelength of about 460 nm.

The patterning in FIG. 6B can be different from the patterning in FIG.4C-2. In FIG. 4C-2, adjacent blue color LEDs are separated with a spacereserved for other color LEDs, and the space has a distance identical totwo drive electrodes with dielectric spacers therebetween on a backplanedevice. Here, it is unnecessary to leave the space for other color LEDs.The blue color LED structure 600 is patterned to form the array of bluecolor LEDs 612 corresponding to pixel circuits of the backplane device.Adjacent blue color LEDs 612 are separated by a gap having a distanceidentical to or smaller than a dielectric spacer. As noted above, thegap should be minimized to increase a pixel filling coefficient whileremaining large enough for isolation spacers to block light cross-talkbetween adjacent LEDs and conductively isolate the adjacent LEDs. A sizeof the gap can be designed to be smaller than and within a dielectricspacer between adjacent drive electrodes in the backplane device. Thus,the patterning of the blue color LED structure 600 can be based on apattern of drive electrodes in the backplane device (or a pattern of thedielectric spacers).

For example, a protective mask can be obtained based on informationfabricating the drive electrodes in the backplane. The drive electrodescan be fabricated by forming a protective mask (e.g., photoresist orhard mask), depositing materials of the drive electrodes, and removingthe protective mask layer. The protective mask for patterning the LEDstructure 600 can be determined based on the protective mask forfabricating the drive electrodes, but with different spacings for LEDs(e.g., even smaller than the drive electrodes), such that the LEDstructure 600 can be selectively etched away during the patterning. Thepatterning can be performed with the following steps: 1) patterning ahard mask layer, e.g., SiNx such as Si₃N₄, on top of the LED structure600, e.g., on the p-electrode layer 606 (e.g., p-GaN) of the LEDstructure 600; 2) etching through the layers of the LED structure 600,to the substrate 601; 3) removing the remaining hard mask layer.

In some implementations, as noted above, differences between differentlight conversion efficiencies among different pixel elements in eachdisplay pixel can be compensated by controlling pixel area ratios amongthe different pixel elements in the display pixel. The LED structure 600can be first patterned to form a plurality of first LEDs to be used asblue sub-pixels for emitting a blue color, then patterned to form aplurality of second LEDs to be used as green sub-pixels for emitting agreen color, and then patterned to form a plurality of third LEDs to beused as red sub-pixels for emitting a red color. An area ratio betweenthe first LED, the second LED, and the third LEDs can be based on aratio of different light conversion efficiencies of the sub-pixels.

As illustrated in FIG. 6B, the LED structure 600 is patterned to form ablue color LED device 610 including an array of blue color LEDs 612.Adjacent blue color LEDs 612 are separated from each other by a gap 611.As noted above, the size of the gap 611 can be predetermined to besmaller than or identical to a size of a dielectric spacer betweenadjacent drive electrodes in a backplane. Each blue color LED 612includes multiple semiconductor layers that include a buffer layer 613,a first contact electrode, e.g., n-GaN electrode 614, light-emittinglayers, e.g., MQW 615, and a second contact electrode, e.g., p-GaNelectrode 616. In some examples, the substrate 601 is a sapphiresubstrate. The LED 612 can have a III-V blue light LED structure, e.g.,the LED structure 412 a in FIG. 4B-3. In some examples, the substrate601 is a silicon substrate. The LED 612 can have a III-V blue light LEDstructure, e.g., the LED structure 412 b in FIG. 4B-4.

FIGS. 6C and 6D are schematic diagrams of an example process of bondingmultiple blue color LED device 610 onto a TFT array backplane device 620and removing LED substrates after the bonding.

The TFT array backplane device 620 can be fabricated on a polyimide film622 on a carrier glass 621, using standard TFT manufacturing processes,e.g., by OEMs. The TFT backplane device 620 can include one or more TFTbackplanes 624 on a top side of the polyimide film 622. Each TFT arraybackplane 624 can include polysilicon layer 625 and integrated circuits(including a number of non-volatile memories and drivers 626) formed onthe polysilicon layers 625. The drivers include scanning drivers, e.g.,the scanning drivers 116 of FIG. 1, and data drivers, e.g., the datadrivers 114 of FIG. 1. Each non-volatile memory is coupled to one of thescanning drivers through at least one word line, e.g., the word line 117of FIG. 1, and to one of the data drivers through at least one bit line,e.g., the bit line 115 of FIG. 1. Each non-volatile memory includes atleast one transistor coupled to a respective drive electrode 627 on topof the TFT array backplane 624. The transistor can have a structuresimilar to that of the transistor 454 a of FIG. 4D-3. Adjacent driveelectrodes 627 are isolated from each other by dielectric spacers 628.

Similar to what discussed above in FIGS. 4I-1 and 4I-2, multiple bluecolor LED devices 600 can be bonded onto the TFT backplane device 620.Each blue color LED device 610 includes an array of blue color LEDs 612formed on an LED substrate 601.

As illustrated in FIG. 6C, a first blue color LED device 610 is flippedover with the p-electrode 616 facing to drive electrodes 627 of pixelcircuits of the TFT backplane 624. The first blue color LED device 610is aligned, e.g., by optically aligning marks, and bonded on driveelectrodes 627 in a first area of the TFT backplane device 620, e.g., bylow temperature direct bonding as described above. The blue color LEDs612 can be bonded to the drive electrodes 627 in the TFT backplanedevice 620.

After the bonding, as illustrated in FIG. 6D, the substrate 601 of thefirst blue color LED device 610 is removed from the blue color LEDs 612that remain bonded on the first area of the backplane device 620. Then asecond blue color LED device 610 is aligned and bonded onto a secondarea of the backplane device 620, the second area being adjacent to thefirst area.

In some examples, the substrate 601 is a sapphire substrate. Thesubstrate 601 of each blue color LED device 610 can be removed by a scanand lift-off process with a laser. Since sapphire is transparent and GaN(the material of the buffer layer 613) is opaque (which absorbs light),a GaN film can be lifted off from the sapphire substrate by a shortpulse KrF UV excimer laser with a wavelength of 248 nm or 308 nm, e.g.,in a power range of 0.4-0.8 J/cm². The short pulse laser is absorbed bythe GaN film to generate a high temperature, e.g., more than 1000° C.Even a brief heating of an interface between the sapphire substrate andthe GaN film to >1000° C. can result in decomposition of GaN into Ga, alow melting-point metal, and nitrogen which remains trapped at theinterface. The sapphire substrate can be cleaned and reused.

In some implementations, one or more blue color LED devices 610 can befirst bonded onto the TFT backplane device 620 and then be removed theLED substrates 601 together. For example, the blue color LED devices 610can have a rectangular (or square) shape and can be bonded onto thebackplane device 620 without or with little gaps therebetween. In someexamples, the LED substrate 601 is a silicon substrate, e.g., a siliconwafer. The LED substrates 601 of the bonded blue color LED devices 610can be removed by chemical wet etching or Chemical Lift-Offs (CLO).

FIG. 6E shows a bonded device 630 obtained by bonding multiple bluecolor LED devices 610 onto the TFT backplane device 620 and thenremoving the LED substrates 601 from the blue color LEDs 612 that remainbonded on the TFT array backplane device 620. Adjacent LEDs 612 areseparated by gaps 611 that can be within the dielectric spacers 628. Thep-GaN contact electrode 616 of each LED 612 is bonded and conductivelycoupled to a respective drive electrode 627 that is conductively coupledto a non-volatile memory 626 of a respective pixel circuit of thebackplane device 620. Thus, each LED 612 is conductively coupled to acorresponding non-volatile memory 626 to form an active-matrix lightemitting sub-pixel.

FIG. 6F is a schematic diagram of a device 640 with isolation spacers642 filled in the bonded device 630 of FIG. 6E. After the bonded device630 is formed, a conductively isolated material can be deposited to fillinto gaps 611 between adjacent LEDs 612 in the bonded device 630 to formthe isolation spacers 642. The isolated material can be an opaquedielectric material or a dielectric material with a light-absorbingmaterial such as a black material, such that light from an LED isblocked or eliminated from propagating to an adjacent LED and thus thereis no or little cross-talk between the adjacent LEDs. The opaquedielectric material can include silicon nitride (SiNx). SiNx can bedeposited in the gaps by chemical vapor deposition (CVD).

Then, topology planarization is performed to remove the buffer layers613 of the LEDs 612 to form a common surface 652 (as illustrated in FIG.6G) with exposure of n-contact electrodes of the LEDs, e.g., n-GaNelectrodes 614 of blue color LEDs 612. For TFT backplane device formedon the carrier glass 621, an etch-back planarization can be carried outby isotropic inductive-coupled plasma etching to remove the isolationmaterial and the epitaxial buffer layers or sacrificial layers to exposethe n-contact electrodes (e.g., n-GaN layers or n-InGaP layers). In somecases, etch-back can be further used for thinning the n-contactelectrodes 614 by etching a portion of the n-contact electrodes 614. Thecommon surface 652 is a surface after the topology planarization and canbe a continuous and flat surface.

FIG. 6G is a schematic diagram of a device 650 including a transparentconductive layer (or a transparent electrode) 654 formed on the commonsurface 652. The transparent conductive layer 654, e.g., an ITO layer,is deposited on top of the common surface 652 including the surfaces ofthe n-contact electrodes of the LEDs 612 to form a common electrode,e.g., an electrical common ground.

FIG. 6H is a schematic diagram of a device 660 with multiple colorphosphor films formed on the device 650 of FIG. 6G. As shown in FIG. 6H,secondary color LEDs, e.g., red color LEDs, green color LEDs, whitecolor LEDs, and/or blue color LEDs can be formed based on thepreviously-formed LEDs, e.g., blue color LEDs 612. The different colorLEDs and corresponding pixel circuits (or non-volatile memories) coupledto the different color LEDs can form multi-color LED pixels 670. Eachpixel 670 can include a blue color LED, a red color LED, a green colorLED, and a white color LED. As discussed above, the secondary color LEDscan be formed on surface of the LEDs 612 by using different colorphosphor materials or different size quantum-dot (QD) materials.

In some implementations, an array of the multi-color LED pixels 670 isformed by the following processes: 1) patterning using photoresist forspecific color LEDs, e.g., red color LEDs; 2) depositing, e.g., byink-jet printing, specific color phosphor films or specific size QDthin-films for the specific color, e.g., red QDs/phosphors 662 (redphosphor films or red QD thin-films); 3) lifting off to remove thephotoresist to form specific color phosphors/Quantum-dot arrays thus toform the specific color LED arrays, e.g., red color LED arrays; 4)repeating the same processes above to form another specific color LEDarrays, e.g., green color LED arrays, but with another specific colorphosphor films or another specific size QD thin-films, e.g., greenQDs/phosphors 664 (green phosphor films or green QD thin-films); and 5)repeating the same processes above to form another specific color LEDarrays, e.g., white LED arrays, but with another specific color phosphorfilms or another specific size QD thin-films, e.g., yellow QDs/phosphors666 (yellow phosphor films or yellow QD thin-films). In some examples,blue color LEDs in the pixels 670 can be also formed by depositingcorresponding blue color phosphor film or corresponding size QD thinfilm 668 on the formed blue color LEDs 612. In some examples,transparent layers 668 are formed on the blue color LEDs 612 in thepixels 670.

Dielectric spacers 669 are formed between the deposited phosphors or QDsfor different color LEDs. The dielectric spacers 669 can include anopaque dielectric material such as SiNx. For example, after depositingthe red QDs/Phosphors 662, green QDs/Phosphors 664, yellow QDs/Phosphors666, and blue QDs/Phosphors or transparent layers 668 on the LEDs 612,the dielectric material is deposited on top of the bonded device.Topology planarization can be performed to form a flat surface acrossthe array of pixels 670.

FIG. 6I is a schematic diagram of a flexible integrated device 680 madefrom the device 660 of FIG. 6H. A polarizer film 682 can be deposited onthe flat surface across the array of pixels 670 and the dielectricspacers 669. The polarizer film 682 is configured to allow light fromthe pixels 670 to propagate through along a polarization direction tobecome a polarized light, which can also reduce scattering and get moreuniform light. A protective layer 684 can be then formed on thepolarizer film 682. As noted above, the protective layer 684 can be atouch-sensitive transparent layer and can form, together with thetransparent layer 654 (as the common electrode), a capacitive touchscreen position sensor. The protective layer 684 can be made oftransparent material, e.g., glass or plastic, coated with a conductivematerial, e.g., indium tin oxide (ITO). To form a flexible device, thecarrier glass 621 can be removed from the backplane device 620, e.g., bylaser lift-off. For example, the polyimide-coated carrier glass 621 canbe delaminated via UV excimer laser lift-off, e.g., at 308 nm, with anablation threshold, e.g., at 235 mJ/cm{circumflex over ( )}2.

Example Processes

FIG. 7 is a flow diagram of an example process of forming an integratedactive-matrix multi-color pixel display system by sequentially bondingdifferent color light emitting elements onto a backplane device. Theintegrated system can be the integrated LED pixel array based displaysystem 100 of FIG. 1, or 300 of FIGS. 3A-3C. The example process 700 canbe similar to the processes described according to the processesdescribed according to FIGS. 4A-1 to 4N.

A plurality of first color light emitting elements is formed on a firstsubstrate (702). Each of the first color light emitting elements isconfigured to emit light with a first color. The plurality of firstcolor light emitting elements can be formed by patterning a first colorlight emitting structure formed on the first substrate. The first colorlight emitting structure can include multiple semiconductor layersepitaxially grown on the first substrate. The plurality of semiconductorlayers can be epitaxial semiconductor layers grown on the substrate,e.g., by MOCVD. For example, the first light emitting structure caninclude a buffer layer, a first contact electrode, e.g., an n-GaNelectrode, multiple quantum well (MQW) semiconductor layers, and asecond contact electrode, e.g., a p-GaN electrode. The MQW layers caninclude Group III-V compounds and be configured to be activated to emitlight with the single color.

In some examples, the MQW layers include pairs of In0.3Ga0.7N/GaNlayers, and the first color light emitting element is a blue color LED,and the first substrate can be a sapphire substrate or a siliconsubstrate. In some examples, the MQW layers include pairs ofIn(0.5)Ga(0.5)N/GaN layers, and the first color light emitting elementis a green color LED, and the first substrate can be a sapphire wafer ora GaN wafer. In some examples, the MQW layers include pairs of InN/GaNlayers, and the first color light emitting element is a red color LED,and the first substrate can be a GaP wafer or a GaN wafer. As notedabove, different color LED arrays can be sequentially boned on thebackplane device. A sequence of the different color LED arrays can be inany suitable order.

The first color light emitting structure can be patterned according toinformation of drive electrodes of pixel circuits on a backplane to beintegrated. Each of the pixel circuits includes a drive electrode in atop layer of the pixel circuit that is in a top layer of the backplane.Adjacent drive electrodes are separated by dielectric spacers. The driveelectrodes can be formed on the backplane by patterning with aprotective mask. The first color light emitting structure can bepatterned based on the protective mask for the drive electrodes.

In some implementations, in the integrated system, adjacent same colorlight emitting elements are separated by two or more other differentcolor light emitting elements along rows and/or columns. Along each rowor column, a distance between adjacent first light emitting elementsformed on the first substrate can be separated by two or more otherdifferent color light emitting elements. Each light emitting element isto be boned with a respective drive electrode on the top layer of thebackplane. Adjacent drive electrodes are separated by one dielectricspacer, thus a distance between adjacent first color light emittingelements can be substantially identical to a distance betweencorresponding pixel circuits for the adjacent first color light emittingelements in the backplane, that is, about two drive electrodes anddielectric spacers therebetween.

During patterning, adjacent first color light emitting elements areseparated from each other by spaces reserved for two or more other colorlight emitting elements. In some cases, the formed first color lightemitting element has a smaller area size than a drive electrode of thebackplane and within an area of the drive electrode. In some cases, aformed first color light emitting element has a same area size as thedrive electrode and can be overlapped on the area of the driveelectrode. In some cases, a formed first color light emitting elementhas a larger area size than the drive electrode but smaller than thedrive electrode and adjacent dielectric spacer, such that the firstcolor light emitting element can have a larger area but be conductivelyisolated from each other. To increase a pixel filling coefficient of theintegrated system, a gap between adjacent light emitting elements can beconfigured to be smaller than or identical to a size of a dielectricspacer between the adjacent drive electrode. Thus, it is preferable forthe first color light emitting element to have a larger area size thanthe drive electrode.

The plurality of first color light emitting elements formed on the firstsubstrate is integrated with the backplane device to form firstsub-pixels of active-matrix multi-color pixels (704). The backplanedevice includes at least one backplane having a plurality of pixelcircuits. Each of the pixel circuits can include a non-volatile memoryincluding at least one transistor conductively coupled to acorresponding drive electrode in a top layer of the backplane device.The plurality of first color light emitting elements can be integratedwith the backplane device by connecting top layers of the first colorlight emitting elements, e.g., the p-contact electrodes, with driveelectrodes in top layers of respective pixel circuits of the backplanedevice, e.g., by low temperature direct bonding. In such a way, each ofthe first color light emitting elements can be conductively coupled to arespective non-volatile memory via the p-contact electrode and the driveelectrode to form a first sub-pixel of an active-matrix multi-colorpixel.

To achieve good bonding, one or more to-be-bonded surfaces can bepre-treated to remove any contamination and to increase adhesion betweenthe surfaces. For example, surfaces of the p-contact electrodes of thefirst color light emitting elements and/or surfaces of the driveelectrodes in the top layer of the backplane device can be pretreatedwith plasma activation.

Before bonding, the plurality of first color light emitting elementsformed on the first substrate are aligned with drive electrodes in thetop layers of the respective pixel circuits in the backplane device, forexample, by optically aligning marks on the substrate and marks on thebackplane device. After the alignment, the two devices are clampedtogether on a bonding chuck, and a pressure is applied on both sides ofthe devices when the devices are in a full contact at a low temperaturefor a period of time. Then the bonded devices can be optionally annealedto another low temperature for another period of time.

The first substrate is removed from the first color light emittingelements that remain integrated on the backplane device (706). The firstsubstrate can be removed by laser lift-off, laser scrubbing, or chemicallift-off.

In some examples, the first color light emitting elements are blue colorLEDs. In some cases, the first substrate can be a sapphire substratethat can be laser lifted-off by a laser, e.g., a short pulse KrF UVexcimer laser, scanning an area over the substrate, e.g., bydelamination of buffer layers (such as GaN layers) of the light-emittingelements from the sapphire substrate transparent for the UV laser. Insome cases, the first substrate is a silicon substrate that can beremoved by chemical lift-off.

In some examples, the first color light emitting elements are greencolor LEDs. The first substrate can be a sapphire substrate that can beremoved by laser lift-off, e.g., by using a short pulse KrF UV excimerlaser.

In some examples, the first color light emitting elements are red colorLEDs. In some cases, the first substrate is a GaP substrate that can beremoved by laser lift-off, e.g., by UV Excimer laser. In some cases, thefirst substrate is a GaAs substrate that can be removed by laserlift-off, e.g., by Nd:YAG Laser, or by chemical lift-off.

In some implementations, the backplane device has a large area andmultiple devices each including first color light emitting elementsformed on first substrates can be bonded onto the backplane device.First color light emitting elements formed on a first substrate can bealigned with respective pixel circuits in a first region of thebackplane device, and then top layers of the first light emittingelements formed on the first substrate are bonded with top layers of therespective pixel circuits that include corresponding drive electrodes.After the bonding, the first substrate can removed by a scan andlift-off process with a laser. Then another first light emittingelements formed on another first substrate can be aligned and bonded ona second region of the backplane device followed by removal of theanother first substrate. The second region can be adjacent to the firstregion.

A plurality of second color light emitting elements is formed on asecond substrate (708). Each of the second color light emitting elementsis configured to emit light with a second color different from the firstcolor. The plurality of second color light emitting elements can beformed in a similar way to the plurality of first color light emittingelements. In some examples, a second color light emitting structure isformed on the second substrate and then is patterned according toinformation of drive electrodes of respective pixel circuits to bebonded. Adjacent second color light emitting elements are also separatedby spacers reserved for two or more other light emitting elements.

Each of the second color light emitting elements includes multiplesemiconductor layers epitaxially grown on the second substrate,including a buffer layer, a first contact electrode, e.g., n-contactelectrode, MQW layers, and a second contact electrode, e.g., p-contactelectrode, as a top layer. The second color light emitting element canhave a height, from the buffer layer to the p-contact electrode. Theheight of the second color light emitting element can be configured tobe higher than the height of the first color light emitting element,such that the second color light emitting elements formed on the secondsubstrate can be touched with surfaces of the backplane device withoutobstruction of the first color light emitting elements that remainbonded on the backplane device.

The plurality of second color light emitting elements formed on thesecond substrate is integrated with the backplane device to form secondsub-pixels of the active-matrix multi-color pixels (710). The pluralityof second color light emitting elements can be integrated with thebackplane device by connecting top layers of the second color lightemitting elements, e.g., the p-contact electrodes, with drive electrodesin top layers of respective pixel circuits of the backplane device,e.g., by low temperature direct bonding. In such a way, each of thesecond color light emitting elements can be conductively coupled to arespective non-volatile memory of the respective pixel circuit via thep-contact electrode and the drive electrode to form a second sub-pixelof the active-matrix multi-color pixel. The bonded second color lightemitting element is adjacent to a corresponding bonded first color lightemitting element on the backplane device. A gap between the adjacentfirst and second color light emitting elements can be smaller than oridentical to a dielectric spacer between adjacent drive electrodes inthe top layer of the backplane device.

To achieve good bonding, one or more to-be-bonded surfaces can bepre-treated to remove any contamination. For example, surfaces of thep-contact electrodes of the second color light emitting elements and/orsurfaces of the drive electrodes in the top layer of the backplanedevice can be pretreated with plasma activation. Before bonding, theplurality of second color light emitting elements formed on the secondsubstrate are aligned with drive electrodes in the top layers of therespective pixel circuits in the backplane device, for example, byoptically aligning marks on the second substrate and marks on thebackplane device. After the alignment, the two devices are clampedtogether on a bonding chuck, and a pressure is applied on both sides ofthe devices when the devices are in a full contact at a low temperaturefor a period of time. Then the bonded devices can be optionally annealedto another low temperature for another period of time.

The second substrate is removed from the second color light emittingelements that remain integrated on the backplane device (712). Similarto the removal of the first substrate, the second substrate can beremoved by laser lift-off, laser scrubbing, or chemical lift-off.

As noted above, the backplane device has a large area and multipledevices each including second color light emitting elements formed onsecond substrates can be bonded onto the backplane device and then thesecond substrate are removed.

In some implementations, a plurality of third color light emittingelements is formed on a third substrate, e.g., similar to the forming ofthe plurality of first color light emitting elements.

Adjacent third color light emitting elements can be separated by spacersreserved for two or more other color light emitting elements. Each ofthe third color light emitting elements is configured to emit light witha third color that is different from the first color and the secondcolor. The third color light emitting element can have a height, fromthe buffer layer to the p-contact electrode. The height of the thirdcolor light emitting element can be configured to be higher than theheight of the first color light emitting element and the height of thesecond color light emitting element, such that the third color lightemitting elements formed on the third substrate can be touched withsurfaces of the backplane device without obstruction of the first andsecond color light emitting elements that remain bonded on the backplanedevice.

Then the plurality of third color light emitting elements formed on thethird substrate is integrated with the backplane device that is bondedwith the first color light emitting elements and the second color lightemitting elements to form third sub-pixels of the active-matrixmulti-color pixels. Each of the third color light emitting elements isconductively coupled to a non-volatile memory of a respective pixelcircuit to form a third sub-pixel by bonding a top layer, e.g., ap-contact electrode, of the third color light emitting element with adrive electrode of the respective pixel circuit. Each of the third colorlight emitting elements bonded on the backplane device is adjacent to acorresponding first color light emitting element and a correspondingsecond light emitting element that are bonded on the backplane device.

Then the third substrate is removed from the third color light emittingelements that remain integrated on the backplane device. Similar to theremoval of the first substrate, the third substrate can be removed bylaser lift-off, laser scrubbing, or chemical lift-off. As noted above,the backplane device has a large area and multiple devices eachincluding third color light emitting elements formed on third substratescan be bonded onto the backplane device and then the third substrate areremoved.

In some implementations, one or more other color light emitting elementscan be integrated with the backplane device to form one or more othersub-pixels of the active-matrix multi-color pixels.

In some implementations, each of the active-matrix multi-color pixelsincludes a first sub-pixel having a first light emitting element and arespective first pixel circuit, a second sub-pixel having a second lightemitting element and a respective second pixel circuit, and a thirdsub-pixel having a third light emitting element and a respective thirdpixel circuit. In a particular example, each of the active-matrixmulti-color pixels includes a red light-emitting diode (LED), a greenLED, and a blue LED. The first, second, and third light emittingelements in each of the active-matrix multi-color pixels can be adjacentand conductively isolated from each other, and the respective first,second, and third pixel circuits can be adjacent and conductivelyisolated from each other. Adjacent drive electrodes in the top layer ofthe backplane device can be isolated by dielectric spacers. Adjacentlight emitting elements, e.g., first and second, second and third, andthird and first, are separated by gaps. A size of a gap can be smallerthan a size of the dielectric spacer.

After the bonding, an isolation material, e.g., an opaque dielectricmaterial such as SiNx, is filled in the gaps between the adjacent lightemitting elements. Then, topology planarization is performed on thelight emitting elements filled with the isolation material to form acommon surface with exposure of first contact electrodes of the first,second, and third light emitting elements, e.g., to the n-contactelectrodes such as n-GaN electrodes.

In some implementations, the backplane includes a low temperaturepolysilicon (LTPS) active-matrix (AM) thin-film transistors (TFT) arraycontrol backplane formed on a flexible film, e.g., a polyimide film or astainless steel, that is formed on a carrier substrate, e.g., a carrierglass. An etch-back planarization can be carried out by isotropicinductive-coupled plasma etching to remove the isolation material andthe epitaxial buffer layers to expose the n-contact electrodes. In somecases, etch-back can be further used for thinning the n-contactelectrodes by etching a portion of the n-contact electrodes.

In some cases, as noted above, in the bonded device, the third colorlight emitting elements can have a higher height than the second colorlight emitting elements that are higher than the first color lightemitting elements. After the etch-back process, surfaces of then-contact electrodes of the third color light emitting elements may behigher than surfaces of the n-contact electrodes of the second colorlight emitting elements that are higher than surfaces of the n-contactelectrodes of the first color light emitting elements. That is, thecommon surface including the surfaces of the n-contact electrodes of thefirst, second, and third light emitting elements can be a continuous andnon-flat surface.

In some implementations, the backplane includes a complementarymetal-oxide-semiconductor (CMOS) backplane formed on a siliconsemiconductor wafer. A CMP (Chemical-Mechanical-Polishing) planarizationcan be carried out to remove the isolation material and the epitaxialbuffer layers to expose n-contact electrodes of the light emittingelements. The CMP planarization can form a continuous and flat surfaceacross the n-contact electrodes of the light emitting elements. The CMPprocess can be further used for thinning the n-contact electrodes of thelight emitting elements by removing a portion of the n-contactelectrodes.

In some implementations, a transparent conductive layer, e.g., an ITOlayer, can be deposited on top of the common surface including thesurfaces of the n-contact electrodes to form a common electrode, e.g.,an electrical common ground, for the first, second, and third lightemitting elements.

In some implementations, a polarizer film can be deposited on thetransparent conductive layer. The polarizer film is configured to allowlight from the light emitting elements to propagate through along apolarization direction to become a polarized light, which can alsoreduce scattering and get more uniform light. A transparent protectivelayer can be then formed on the polarizer film. The transparentprotective layer can be a touch-sensitive transparent layer and canform, together with the transparent conductive layer, a capacitive touchscreen position sensor. The transparent protective layer can be made oftransparent material, e.g., glass or plastic, coated with a conductivematerial such as ITO.

In some implementations, the backplane device is a TFT array controlbackplane formed on a flexible film on a carrier glass. After themulti-color active matrix display pixels is formed, the carrier glasscan be removed, e.g., by laser lift-off. For example, thepolyimide-coated carrier glass can be delaminated via UV excimer laserlift-off at 308 nm. In such a way, the formed integrated device on theflexible film can be flexible.

FIG. 8 is a flow diagram of an example process 800 of forming anintegrated active-matrix multi-color pixel display system by firstbonding single color light emitting elements onto a backplane device andthen depositing multiple color phosphors or quantum dots (QDs)materials. The integrated system can be the integrated LED pixel arraybased display system 100 of FIG. 1, or 500 of FIGS. 5A-5B. The exampleprocess 800 can be similar to the processes described according to theprocesses described according to FIGS. 6A-6I.

A plurality of light emitting elements is formed on a substrate (802).Each of the light emitting elements is operable to emit light with asingle color. The plurality of light emitting elements can be formed bypatterning a light emitting structure formed on the substrate. The lightemitting structure can include multiple semiconductor layers epitaxiallygrown on the substrate. For example, the light emitting structure caninclude multiple quantum well (MQW) semiconductor layers between a firstcontact electrode, e.g., a p-GaN electrode, and a second contactelectrode, e.g., an n-GaN electrode. The MQW layers can include GroupIII-V compounds and be configured to be activated to emit light with thesingle color. In some examples, the MQW layers include pairs ofIn0.3Ga0.7N/GaN layers, and the light emitting structure is a blue colorLED structure, and the substrate can be a sapphire substrate or asilicon substrate. In some examples, the MQW layers include pairs ofAlGaN/GaN layers, and the light emitting structure can be a UV or deepUV LED structure formed on a sapphire substrate. The plurality of layerscan be epitaxial semiconductor layers grown on the substrate, e.g., byMOCVD.

The light emitting structure can be patterned according to informationof drive electrodes of pixel circuits on a backplane to be integrated.Each of the pixel circuits includes a drive electrode in a top layer ofthe pixel circuit that is in a top layer of the backplane. Adjacentdrive electrodes are separated by dielectric spacers. The driveelectrodes can be formed on the backplane by patterning with aprotective mask. The light emitting structure can be patterned accordingto the protective mask for the drive electrodes. A distance betweenadjacent light emitting elements on the substrate can be substantiallyidentical to a distance between adjacent drive electrodes in thebackplane. Also, to increase a pixel filling coefficient of theintegrated system, a gap between adjacent light emitting elements can beconfigured to be smaller than or identical to a size of a dielectricspacer between the adjacent drive electrode.

The plurality of light emitting elements formed on the substrate isintegrated with the backplane device to form a plurality ofactive-matrix light emitting pixels (804). The backplane device includesat least one backplane having a plurality of pixel circuits. Each of thepixel circuits can include a non-volatile memory including at least onetransistor conductively coupled to a corresponding drive electrode in atop layer of the backplane device. The plurality of light emittingelements can be integrated with the backplane device by connecting toplayers of the light emitting elements, e.g., the first contactelectrodes, with drive electrodes in top layers of respective pixelcircuits of the backplane device, e.g., by low temperature directbonding. In such a way, each of the light emitting elements can beconductively coupled to a respective non-volatile memory via the firstcontact electrode and the drive electrode.

To achieve good bonding, one or more to-be bonded surfaces can bepre-treated to remove any contamination. For example, surfaces of thefirst contact electrodes of the light emitting elements and/or surfacesof the drive electrodes in the top layer of the backplane device can bepretreated with plasma activation.

Before bonding, the plurality of light emitting elements formed on thesubstrate are aligned with drive electrodes in the top layers of therespective pixel circuits in the backplane device, for example, byoptically aligning marks on the substrate and marks on the backplanedevice. After the alignment, the two devices are clamped together on abonding chuck, and a pressure is applied on both sides of the deviceswhen the devices are in a full contact at a low temperature for a periodof time. Then the bonded devices can be optionally annealed to anotherlow temperature for another period of time.

The substrate is removed from the light emitting elements that remainintegrated on the backplane device (806). In some examples, thesubstrate is a sapphire substrate that can be laser lifted-off by alaser, e.g., a short pulse KrF UV excimer laser, scanning an area overthe substrate, e.g., by delamination of buffer layers (such as GaNlayers) of the light-emitting elements from the sapphire substratetransparent for the UV laser. In some examples, the substrate is asilicon substrate that can be removed by chemical lift-off.

In some implementations, the backplane device has a large area andmultiple devices each including light emitting elements formed onsubstrates can be bonded onto the backplane device. Light emittingelements formed on a first substrate can be aligned with respectivepixel circuits in a first region of the backplane device, and then toplayers of the light emitting elements formed on the first substrate arebonded with top layers of the respective pixel circuits that includecorresponding drive electrodes. After the bonding, the first substratecan removed by scanning by using a laser an area on the first substratesuch that the light emitting elements in the area are separated from thefirst substrate and remain bonded on the backplane device and liftingoff the first substrate from the light emitting elements that remainbonded on the backplane device. Then light emitting elements formed on asecond substrate can be aligned and bonded on a second region of thebackplane device followed by removal of the second substrate. The secondregion can be adjacent to the first region, and the light emittingelements bonded on the second region are adjacent to the light emittingelements bonded on the first region.

After the bonding, an isolation material, e.g., an opaque dielectricmaterial such as SiNx, is filled in gaps between the adjacent lightemitting elements. Then, topology planarization is performed on thelight emitting elements filled with the isolation material to form acommon surface across the light emitting elements with exposure ofsecond contact electrodes of the light emitting elements, e.g., to thesecond contact electrodes such as n-GaN electrodes. The common surfacecan be a continuous and flat surface.

In some implementations, the backplane includes a low temperaturepolysilicon (LTPS) active-matrix (AM) thin-film transistors (TFT) arraycontrol backplane formed on a flexible film, e.g., a polyimide film or astainless steel, that is formed on a carrier substrate, e.g., a carrierglass. An etch-back planarization can be carried out by isotropicinductive-coupled plasma etching to remove the isolation material andthe epitaxial buffer layers to expose the n-contact electrodes. In somecases, etch-back can be further used for thinning the n-contactelectrodes by etching a portion of the n-contact electrodes.

In some implementations, the backplane includes a complementarymetal-oxide-semiconductor (CMOS) backplane formed on a siliconsemiconductor wafer. A CMP (Chemical-Mechanical-Polishing) planarizationcan be carried out to remove the isolation material and the epitaxialbuffer layers to expose n-contact electrodes of the light emittingelements. The CMP planarization can form a continuous and flat surfaceacross the n-contact electrodes of the light emitting elements. The CMPprocess can be further used for thinning the n-contact electrodes of thelight emitting elements by removing a portion of the n-contactelectrodes.

A transparent conductive layer, e.g., an ITO layer, can be deposited ontop of the common surface including the surfaces of the second contactelectrodes to form a common electrode, e.g., an electrical commonground, for the light emitting elements.

An array of active-matrix multi-color display pixels is formed byselectively depositing different color phosphor or different sizequantum-dot materials on the light emitting elements (808). Each lightemitting element is operable to emit light with a single color. Thephosphor material or the quantum-dot material is operable to emit asecondary color when excited by light from the light-emitting element.The secondary color can be different from the single color.

In some implementations, each light emitting element is operable as ablue color LED, e.g., with an emission wavelength between 450 nm and 500nm. In each display pixel, at least two blue color LEDs are configuredto optically excite at least two other colors by secondary lightemission of the phosphor materials or quantum dots materials on the atleast two blue color LEDs. Each of the active-matrix light emittingpixels is configured to be a multi-color display pixel including oneblue color LED operable to provide a blue color and the at least twoblue color LEDs with the phosphor materials or quantum dots materialsoperable to respectively provide a red color and a green color.

In some implementations, each of the light-emitting elements is operableas a light-emitting diode (LED) to emit UV or deep UV light with awavelength between 100 nm and 450 nm. For each of the active-matrixlight emitting pixels, at least three UV or deep UV LEDs are configuredto optically excite at least three colors, e.g., red, green, and blue,by secondary light emission of the phosphor materials or quantum dotsmaterials on the at least three UV or deep UV LEDs. The pixel can alsoinclude a UV or deep UV LED configured to emit a white color bysecondary light emission of yellow color phosphor material or quantumdot material on the UV or deep UV LED.

A transparent protective layer can be formed on top of the array ofactive-matrix multi-color display pixels. The protective layer can be atouch-sensitive protective layer and can form, together with thetransparent conductive layer (as the common electrode), a capacitivetouch screen position sensor. The protective layer can be made oftransparent material, e.g., glass or plastic, coated with a conductivematerial, e.g., indium tin oxide (ITO). A polarizer film can bedeposited between the protective layer and the array of display pixels.

In some implementations, the backplane device is a TFT array controlbackplane formed on a flexible film on a carrier glass. After themulti-color active matrix display pixels is formed, the carrier glasscan be removed, e.g., by laser lift-off. For example, thepolyimide-coated carrier glass can be delaminated via UV excimer laserlift-off at 308 nm. In such a way, the formed integrated device on theflexible film can be flexible.

Embodiments of the subject matter and the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, in tangibly-embodied computer software or firmware, incomputer hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Embodiments of the subject matter described in thisspecification can be implemented as one or more computer programs, i.e.,one or more modules of computer program instructions encoded on atangible non-transitory program carrier for execution by, or to controlthe operation of, data processing apparatus. Alternatively or inaddition, the program instructions can be encoded on anartificially-generated propagated signal, e.g., a machine-generatedelectrical, optical, or electromagnetic signal, that is generated toencode information for transmission to suitable receiver apparatus forexecution by a data processing apparatus. The computer storage mediumcan be a machine-readable storage device, a machine-readable storagesubstrate, a random or serial access memory device, or a combination ofone or more of them.

The processes and logic flows described in this specification can beperformed by one or more programmable computers executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Computers suitable for the execution of a computer program include, byway of example, can be based on general or special purposemicroprocessors or both, or any other kind of central processing unit.Generally, a central processing unit will receive instructions and datafrom a read-only memory or a random access memory or both. The essentialelements of a computer are a central processing unit for performing orexecuting instructions and one or more memory devices for storinginstructions and data. Generally, a computer will also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto-optical disks, or optical disks. However, a computer need nothave such devices. Moreover, a computer can be embedded in anotherdevice, e.g., a mobile telephone, a personal digital assistant (PDA), amobile audio or video player, a game console, a Global PositioningSystem (GPS) receiver, or a portable storage device, e.g., a universalserial bus (USB) flash drive, to name just a few.

Computer-readable media suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto-optical disks; andCD-ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinvention or on the scope of what may be claimed, but rather asdescriptions of features that may be specific to particular embodimentsof particular inventions. Certain features that are described in thisspecification in the context of separate embodiments can also beimplemented in combination in a single embodiment. Conversely, variousfeatures that are described in the context of a single embodiment canalso be implemented in multiple embodiments separately or in anysuitable subcombination. Moreover, although features may be describedabove as acting in certain combinations and even initially claimed assuch, one or more features from a claimed combination can in some casesbe excised from the combination, and the claimed combination may bedirected to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various system modulesand components in the embodiments described above should not beunderstood as requiring such separation in all embodiments.

Thus, particular embodiments of the subject matter have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the subject matter.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method of fabricating an integrated device, comprising: forming a plurality of first light emitting elements on a first substrate, each of the first light emitting elements comprising first semiconductor layers epitaxially grown on the first substrate and being configured to emit light with a first color, the first semiconductor layers comprising a first conductive outer layer on a side of the first semiconductor layers further from the first substrate; integrating the first light emitting elements formed on the first substrate with a backplane device having a plurality of pixel circuits by bonding the first conductive outer layers of the first light emitting elements with conductive outer layers of first pixel circuits in the plurality of pixel circuits such that each of the first light emitting elements is bonded and conductively coupled to a first pixel circuit in the backplane device, wherein the plurality of pixel circuits are conductively isolated from each other; and then after integrating the first light emitting elements, removing the first substrate from the first light emitting elements that remain integrated with the backplane device.
 2. The method of claim 1, wherein integrating the first light emitting elements on the first substrate with the backplane device comprises: before the bonding, pretreating with plasma activation at least one of surfaces of the first conductive outer layers of the first light emitting elements or a surface of the backplane device comprising surfaces of the conductive outer layers of the first pixel circuits.
 3. The method of claim 1, wherein forming a plurality of first light emitting elements on a first substrate comprises: patterning a first light emitting structure formed on the first substrate to form the plurality of first light emitting elements, wherein the first light emitting structure comprises the first semiconductor layers epitaxially grown on the first substrate.
 4. The method of claim 3, wherein patterning a first light emitting structure formed on the first substrate to form the plurality of first light emitting elements comprises: patterning the first light emitting structure formed on the first substrate according to a pattern of the first pixel circuits in the backplane device, such that each of the first light emitting elements is aligned and bonded on top of the first pixel circuit in the backplane device.
 5. The method of claim 1, wherein integrating the first light emitting elements on the first substrate with the backplane device comprises: directly bonding surfaces of the first conductive outer layers of the first light emitting elements with surfaces of conductive outer layers of the first pixel circuits.
 6. The method of claim 1, further comprising: before the integrating, aligning the first light emitting elements with the first pixel circuits.
 7. The method of claim 6, wherein aligning the first light emitting elements with the first pixel circuits comprises: aligning the first light emitting elements on the first substrate with the first pixel circuits in a first region of the backplane device, wherein integrating the first light emitting elements on the first substrate with the backplane device comprises: bonding the first light emitting elements on the first substrate with the first pixel circuits in the first region of the backplane device, and wherein the method further comprises: bonding another plurality of first light emitting elements on another first substrate with respective another first pixel circuits in a second region of the backplane device, the second region being adjacent to the first region; and removing the another first substrate from the another plurality of first light emitting elements that remain bonded on the backplane device.
 8. The method of claim 1, wherein removing the first substrate from the first light emitting elements comprises: scanning, by using a laser, an area on the first substrate such that the first light emitting elements in the area are separated from the first substrate and bonded on the backplane device; and lifting off the first substrate from the first light emitting elements that remain bonded on the backplane device.
 9. The method of claim 1, wherein a size of the first light emitting element is no smaller than a size of the first pixel circuit.
 10. The method of claim 1, wherein each of the pixel circuits comprises a non-volatile memory including at least one transistor conductively coupled to a corresponding drive electrode that is a conductive outer layer of the pixel circuit, the corresponding drive electrodes in adjacent pixel circuits being separated by dielectric spacers, and wherein each of the first light emitting elements comprises a corresponding contact electrode as the first conductive outer layer, and wherein each of the first light emitting elements is conductively coupled to a non-volatile memory in the first pixel circuit through a corresponding contact electrode and a corresponding drive electrode of the first pixel circuit.
 11. The method of claim 1, further comprising: forming a plurality of second light emitting elements on a second substrate, each of the second light emitting elements comprising second semiconductor layers epitaxially grown on the second substrate an being configured to emit light with a second color different from the first color, the second semiconductor layers comprising a second conductive outer layer on a side of the second semiconductor layers further from the second substrate; integrating the second light emitting elements formed on the second substrate with the backplane device by bonding the second conductive outer layers of the second light emitting elements with conductive outer layers of second pixel circuits in the plurality of pixel circuits, such that each of the second light emitting elements is bonded and conductively coupled to a second pixel circuit that is adjacent to a corresponding first pixel circuit in the backplane device; and then after integrating the second light emitting elements, removing the second substrate from the second light emitting elements that remain integrated with the backplane device, wherein each of the second light emitting elements is adjacent to a corresponding first light emitting element on the backplane device.
 12. The method of claim 11, wherein a height of each of the second light emitting elements formed on the second substrate is larger than or identical to a height of each of the first light emitting elements formed on the first substrate.
 13. The method of claim 11, wherein a distance between adjacent second light emitting elements on the backplane device is substantially identical to a distance between adjacent second pixel circuits in the backplane device, and wherein a distance between adjacent first and second light emitting elements is smaller than or identical to a distance between adjacent pixel circuits in the backplane device.
 14. The method of claim 11, further comprising: forming a plurality of third light emitting elements on a third substrate, each of the third light emitting elements comprising third semiconductor layers epitaxially grown on the third substrate and being configured to emit light with a third color that is different from the first color and the second color, the third semiconductor layers comprising a third conductive outer layer on a side of the third semiconductor layers further from the third substrate; integrating the third light emitting elements formed on the third substrate with the backplane device by bonding the third conductive outer layers of the third light emitting elements with conductive outer layers of third pixel circuits in the plurality of pixel circuits, such that each of the third light emitting elements is bonded and conductively coupled to a third pixel circuit that is adjacent to a corresponding first pixel circuit and a corresponding second pixel circuit in the backplane device; and then after integrating the third light emitting elements, removing the third substrate from the third light emitting elements that remain integrated with the backplane device, wherein each of the third light emitting elements on the backplane device is adjacent to a corresponding first light emitting element and a corresponding second light emitting element on the backplane device.
 15. The method of claim 14, wherein a height of each of the third light emitting elements formed on the third substrate is larger than or identical to a height of each of the second light emitting elements formed on the second substrate that is larger than or identical to a height of each of the first light emitting elements formed on the first substrate.
 16. The method of claim 14, wherein the first light emitting elements are conductively connected to the first pixel circuits to form first sub-pixels of active-matrix multi-color pixels, wherein the second light emitting elements are conductively connected to the second pixel circuits to form second sub-pixels of the active-matrix multi-color pixels, wherein the third light emitting elements are conductively connected to the third pixel circuits to form third sub-pixels of the active-matrix multi-color pixels, wherein each of the active-matrix multi-color pixels comprises a first sub-pixel having a first light emitting element and a first pixel circuit, a second sub-pixel having a second light emitting element and a second pixel circuit, and a third sub-pixel having a third light emitting element and a third pixel circuit, and wherein the first, second, and third light emitting elements in each of the active-matrix multi-color pixels are adjacent and conductively isolated from each other, and the respective first, second, and third pixel circuits are adjacent and conductively isolated from each other.
 17. The method of claim 16, wherein each of the active-matrix multi-color pixels comprises a red light-emitting diode (LED), a green LED, and a blue LED.
 18. The method of claim 14, further comprising: filling an isolation material in gaps between adjacent first, second and third light emitting elements that remain integrated on the backplane device, wherein the isolation material comprises an opaque and conductively isolated dielectric material.
 19. The method of claim 18, wherein each of the first, second, third light emitting elements comprises a first contact electrode as a conductive outer layer of the light emitting element and a second contact electrode formed on a buffer layer that is formed on a corresponding substrate, and wherein the method further comprises: planarizing the first, second, third light emitting elements with the isolation material filled in the gaps to remove the buffer layers to form a common surface with exposure of the second contact electrodes of the first, second, third light emitting elements.
 20. The method of claim 19, further comprising: forming a transparent conductive layer on the common surface to form a common electrode for the first, second, and third light emitting elements.
 21. A method of fabricating an integrated active-matrix multi-color pixel array based display, the method comprising: forming a plurality of light emitting elements on a semiconductor substrate, each of the light emitting elements comprises multiple semiconductor layers epitaxially grown on the semiconductor substrate and being configured to emit light with a first color, the semiconductor layers including one or more quantum well layers having Group III-V compounds between a first doped semiconductor layer as a first contact electrode and a second doped semiconductor layer as a second contact electrode; integrating the light emitting elements on the semiconductor substrate with a backplane device to form a plurality of active-matrix light emitting pixels by conductively connecting the first contact electrode of each of the light emitting elements with a drive electrode of a respective pixel circuit in the backplane device, wherein the backplane device comprises at least one backplane having a plurality of pixel circuits that are conductively isolated from each other, each of the pixel circuits comprising a non-volatile memory conductively coupled to the drive electrode of the pixel circuit, wherein each of the active-matrix pixels comprises at least one of the light emitting element and at least one of the non-volatile memories conductively coupled to the at least one of the light emitting elements, then removing the semiconductor substrate from the light emitting elements that remain integrated on the backplane device; and forming an array of active-matrix multi-color display pixels by selectively depositing at least one phosphor film or quantum dots film on at least one light emitting element in each of the active-matrix light emitting pixels, the at least one phosphor film or quantum dots film being operable to emit a secondary light when excited by the light with the first color from the at least one light emitting element, wherein the secondary light has a second color different from the first color.
 22. The method of claim 21, further comprising: after removing the semiconductor substrate from the light emitting elements, forming first isolation spacers between adjacent light emitting elements, the first isolation spacers including an opaque conductively isolated dielectric material; planarizing the light emitting elements with the first isolation spacers to expose the second contact electrodes of the light emitting elements and to form a common surface across the second contact electrodes of the light emitting elements; depositing a transparent conductive layer on the common surface to form a common electrode for the light emitting elements integrated on the backplane device, wherein the at least one phosphor film or quantum dots film is selectively formed on the transparent conductive layer; forming second isolation spacers between adjacent pixel elements of the active-matrix multi-color display pixels and on the transparent conductive layer, the second isolation spacers comprising the opaque conductively isolated dielectric material; and forming a transparent protective layer on top of the active-matrix multi-color display pixels and the second isolation spacers. 